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Antibiotics

Antibiotics

Definition

Antibiotics are drugs that are used to treat infections caused by bacteria and other organisms, including protozoa, parasites, and fungi.

Purpose

Many treatments for cancer destroy disease-fighting white blood cells, thereby reducing the body's ability to fight infection. For example, bladder, pulmonary, and urinary tract infections may occur with chemotherapy . Single-celled organisms called protozoa are rarely a problem for healthy individuals. However, they can cause serious infections in individuals with low white blood cell counts. Because of the dangers that infections present for cancer patients, antibiotic treatment often is initiated before the exact nature of the infection has been determined; instead, the choice of antibiotic may depend on the site of the infection and the organism that is likely to be the cause. Often, an antibiotic that kills a broad spectrum of bacteria is chosen and several antibiotics may be used together.

Description

The common antibiotics that are used during cancer treatment include:

  • Atovaquone (Mapren): antiprotozoal drug used to prevent and treat a very serious type of pneumonia called Pneumocystis carinii pneumonia (PCP), in individuals who experience serious side effects with SMZ-TMP (Sulfamethoxazole/Trimethoprim, brand name Bactrim).
  • Aztreonam (Azactam): monobactam antibiotic used to treat gram-negative bacterial infections of the urinary and lower respiratory tracts and the female organs, and infections that are present throughout the body (systemic infections or septicemia).
  • Cefepime (Maxipime), ceftazidime (Ceptaz, Fortaz, Tazicef, Tazidime), and ceftriaxone sodium (Rocephin): members of a group of antibiotics called cephalosporins used to treat bacterial infections of the urinary and lower respiratory tracts, and infections of the skin, bones, joints, pelvis, and abdomen.
  • Ciprofloxacin (Cipro): fluoroquinolone antibiotic used to treat certain gram-negative and gram-positive bacteria and some mycobacteria.
  • Clindamycin phosphate (Cleocin): used to treat gram-positive and gram-negative bacterial infections and, in individuals who are allergic to sulfadiazine, toxoplasmosis caused by a parasitic protozoa.
  • Gentamicin (gentamycin) sulfate (generic name product, Garamycin, G-Mycin, Jenamicin): aminoglycoside antibiotic used to treat serious infections by many gram-negative bacteria that cannot be treated with other medicines.
  • Metronidazole hydrochloride (Flagyl, Metric 21, Metro I.V., Protostat): used for anaerobic bacteria and protozoa.
  • Pentamidine (generic name product, Pentam 300): used to treat PCP if serious side effects develop with SMZTMP.
  • Pyrimethamine (Daraprim): antiprotozoal medicine used together with sulfadiazine to treat toxoplasmosis; or in combination with other medicines for treating mild to moderate PCP, in individuals who cannot tolerate the standard treatment.
  • Sulfadiazine (generic name product): sulfonamide antibiotic used with pyrimethamine to treat toxoplasmosis.
  • Sulfamethoxazole-Trimethoprim (SMZ-TMP) (generic name product, Bactrim, Cofatrim Forte, Cotrim, Septra, Sulfatrim): the sulfonamide antibiotic, sulfamethoxazole, used in combination with trimethoprim, to prevent and treat PCP and bacterial infections, such as bronchitis and middle ear and urinary tract infections.
  • Trimethoprim (generic name product, Proloprim, Trimpex): primarily used to prevent or treat urinary tract infections.
  • Vancomycin hydrochloride (generic name product, Vancocin): glycopeptide antibiotic used to treat a variety of serious gram-positive bacterial infections for which other medicines are ineffective, including strains of Staphylococcus that are resistant to most oral antibiotics.

Most of these antibiotics kill bacteria by preventing them from making protein for their cell walls. Ciprofloxacin and metronidazole prevent bacteria from reproducing by interfering with their ability to make new DNA. All of these drugs are approved for prescription by the U.S. Food and Drug Administration.

Recommended dosage

Dosages of antibiotics depend on the individual, the infection that is being treated, and the presence of other medical conditions. For children, the dosage usually is based on body weight and is lower than the adult dosage. To be effective, an entire treatment with antibiotics must be completed, even if the symptoms of infection have disappeared. Furthermore, it is important to keep the level of antibiotic in the body at a constant level during treatment. Therefore, the drug should be taken on a regular schedule. If a dose is missed, it should be taken as soon as possible. If it is almost time for the next dose, the missed dose should be skipped. Doubling up doses is generally not recommended.

Average adult dosages of common antibiotics for cancer patients are as follows:

  • Atovaquone: for PCP treatment, 750 mg oral suspension twice a day, or tablets three times per day, for 21 days; for PCP prevention, 1, 500 mg oral suspension, once a day; must be taken with balanced meals.
  • Aztreonam: 1-2 gm every 6-12 hours, injected into a vein, over a 20-60 minute-period.
  • Cefepime: 500 mg to 2 gm, injected into a vein or muscle, every 8-12 hours for 7-10 days.
  • Ceftazidime: 250 mg to 2 gm, injected into a vein or muscle, every 8-12 hours.
  • Ceftriaxone: 1-2 gm, injected into a vein or muscle, every 24 hours.
  • Ciprofloxacin: 500-750 mg of the tablet or suspension, every 12 hours, for 3-28 days, taken two hours after meals with 8 oz of water; bone and joint infections usually are treated for at least 4-6 weeks; 200-400 mg injected every 8-12 hours.
  • Clindamycin: 150-300 mg of capsule or solution, every six hours; 300-600 mg every six to eight hours or 900 mg every eight hours, injected into a vein or muscle.
  • Gentamicin: dosage determined by body weight, every 8-24 hours for at least 7-10 days, injected into a vein or muscle.
  • Metronidazole: for bacterial infections, 7.5 mg per kg (3.4 mg per lb) of body weight up to a maximum of 1 gm, every six hours for at least seven days (capsules or tablets); 15 mg per kg (6.8 mg per lb) for the first dose, followed by half that dosage every six hours for at least seven days (injected into a vein); for protozoal infections caused by amebas, 500-750 mg of oral medicine, three times per day for 5-10 days; for trichomoniasis, 2 gm for one day or 250 mg three times per day for seven days (oral medicine); extended-release tablets for vaginal bacterial infections, 750 mg once a day for seven days.
  • Pentamidine: for treating PCP, 4 mg per kg (1.8 mg per lb) of body weight, once per day for 14-21 days, injected into a vein over one to two hours, while lying down.
  • Pyrimethamine: for toxoplasmosis, 25-200 mg tablets, taken with other medicine, for several weeks.
  • Sulfadiazine: for bacterial and protozoal infections, 2-4 gm for the first dose, followed by 1 gm every four to six hours (tablets).
  • SMZ-TMP: 800 mg of sulfamethoxazole and 160 mg of trimethoprim, (tablet or oral suspension), every 12 hours for bacterial infections and every 24 hours for prevention of PCP; dosage based on body weight for PCP treatment; injections based on body weight, every six, eight or 12 hours for bacterial infections and every six hours for PCP treatment.
  • Trimethoprim: 100 mg tablet every 12 hours for 10 days; for prevention of urinary tract infections, once a day for a long period.
  • Vancomycin: 7.5 mg per kg (3.4 mg per lb) of body weight, or 500 mg-1 gram, injected or taken orally, every 6-12 hours.

Precautions

Stomach or intestinal problems or colitis (inflammation of the colon) may affect the use of:

  • Atovaquone
  • Cephalosporins
  • Clindamycin

Kidney or liver disease may affect the use of:

  • Aztreonam
  • Cefepime
  • Ceftazidime
  • Ciprofloxacin
  • Clindamycin
  • Gentamicin
  • Metronidazole
  • Pentamidine
  • Pyrimethamine
  • Sulfadiazine
  • SMZ-TMP
  • Trimethoprim
  • Vancomycin

Central nervous system or seizure disorders may affect the use of:

  • Ciprofloxacin
  • Metronidazole
  • Pyrimethamine

Anemia (low red blood cell count) or other blood disorders may affect the use of:

  • Metronidazole
  • Pentamidine
  • Pyrimethamine
  • Sulfadiazine
  • SMZ-TMP
  • Trimethoprim

Ciprofloxacin may not be suitable for individuals with tendinitis or with skin sensitivities to sunlight. Gentamicin may not be suitable for people with hearing problems, myasthenia gravis , or Parkinson's disease. Metronidazole may not be suitable for individuals with heart disease, oral or vaginal yeast infections, or a history of alcoholism. Pentamidine may not be suitable for individuals with heart disease, bleeding disorders, or low blood pressure. Pentamidine may affect blood sugar levels, making control of diabetes mellitus or hypoglycemia (low blood sugar) difficult. Vancomycin may not be appropriate for individuals with hearing problems.

Many antibiotics should not be taken during pregnancy or while breast-feeding. Older individuals may be more susceptible to the side effects of sulfadiazine, SMZ-TMP, or trimethoprim.

Side effects

Some individuals may have allergic reactions to antibiotics. If symptoms of an allergic reaction (such as rash, shortness of breath, swelling of the face and neck), severe diarrhea , or abdominal cramping occur, the antibiotic should be stopped and the individual should seek medical advice.

Because antibiotics can affect bacteria that are beneficial, as well as those that are harmful, women may become susceptible to infections by fungi when taking antibiotics. Vaginal itching or discharge may be symptoms of such infections. All patients may develop oral fungal infections of the mouth, indicated by white plaques in the mouth.

Injected antibiotics may result in irritation, pain, tenderness, or swelling in the vein used for injection. Antibiotics used in cancer patients may have numerous side effects, both minor and severe; however, most side effects are uncommon or rare.

The more common side effects of atovaquone, aztreonam, cephalosporins, ciprofloxacin, clindamycin, gentamicin, metronidazole, and SMZ-TMP include:

  • nausea and vomiting
  • diarrhea
  • loss of appetite

Eating active cultured yogurt may help counteract diarrhea, but if a patient has low white blood cells, this remedy is not recommended. For mild diarrhea with cephalosporins, only diarrhea medicines containing kaolin or attapulgite should be taken. With clindamycin, diarrhea medicines containing attapulgite should be taken several hours before or after the oral antibiotic. Diarrhea following antibiotics like clindamycin may indicate a bacterial infection that needs additional therapy, and a physician should be consulted.

Other side effects of atovaquone may include:

  • fever
  • skin rash
  • cough
  • headache
  • insomnia

Other side effects of ciprofloxacin may include:

  • abdominal pain
  • increase in blood tests for kidney function
  • dizziness or light-headedness
  • inflammation or tearing of a tendon
  • drowsiness
  • insomnia

Other common side effects of clindamycin include abdominal pain and fever. Side effects may occur up to several weeks after treatment with this medicine.

Gentamicin and vancomycin may cause serious side effects, particularly in elderly individuals and newborn infants. These include kidney damage and damage to the auditory nerve that controls hearing. Other, more common side effects of gentamicin may include:

  • changes in urination
  • increased thirst
  • muscle twitching or seizures
  • headache
  • lethargy

When gentamicin is injected into a muscle, vein, or the spinal fluid, the following side effects may occur:

  • leg cramps
  • skin rash
  • fever
  • seizures

Side effects from gentamicin may develop up to several weeks after the medicine is stopped.

More common side effects of metronidazole include:

  • mouth dryness
  • unpleasant or metallic taste
  • dizziness or light-headedness
  • headache
  • stomach pain

Sugarless candy or gum, bits of ice, or a saliva substitute may relieve symptoms of dry mouth.

Pentamidine, pyrimethamine, sulfonamides, SMZTMP, and trimethoprim can lower the number of white blood cells, resulting in an increased risk of infection. These drugs also can lower the number of blood platelets that are important for blood clotting. Thus, there is an increased risk of bleeding or bruising while taking these drugs.

Serious side effects of pentamidine may include:

  • heart problems
  • low blood pressure
  • high or low blood sugar
  • other blood problems
  • decrease in urination
  • sore throat and fever
  • sharp pain in upper abdomen

Some of these symptoms may not occur until several months after treatment with pentamidine.

Pyrimethamine and trimethoprim may lower the red blood cell count, causing anemia. Leucovorin or the vitamin folic acid may be prescribed for anemia.

Some individuals become more sensitive to sunlight when taking sulfonamides, SMZ-TMP, or trimethoprim. Other common side effects of sulfonamides and SMZTMP include:

  • dizziness
  • itching
  • skin rash
  • headache
  • mouth sores or swelling of the tongue
  • fatigue

If vancomycin is injected into a vein too quickly, it can cause flushing and a rash over the neck, face, and chest, wheezing or difficulty breathing, and a dangerous decrease in blood pressure.

Interactions

Many prescription and non-prescription medicines can interact with these antibiotics. Therefore, it is important to consult a complete list of known drug interactions. Among the more common or dangerous interactions:

  • Antibiotics that lower the number of blood platelets, with blood thinners (anticoagulants), such as warfarin
  • Aztreonam and metronidazole with alcohol; it is important not to consume alcohol until at least three days after treatment with these antibiotics
  • Ciprofloxacin with antacids, iron supplements, or caffeine
  • Pentamidine or pyrimethamine with previous treatments with x rays or cancer medicines (increased risk of blood cell damage)
  • Trimethoprim with diuretics to remove excess fluid in the elderly

Many medicines can increase the risk of hearing or kidney damage from gentamicin. These include:

  • cisplatin
  • combination pain medicine with acetaminophen and aspirin or other salicylates (taken regularly in large amounts)
  • cyclosporine
  • inflammation or pain medicine, except narcotics
  • lithium
  • methotrexate
  • other medicines for infection

The following drugs may increase the risk of liver effects with sulfadiazine or SMZ-TMP:

  • acetaminophen, long-term, high-dose (eg Tylenol)
  • birth control pills containing estrogens
  • disulfiram (Antabuse)
  • other medicines for infection

Resources

BOOKS

American Cancer Society. Consumers Guide to Cancer Drugs.Atlanta: Jones and Bartlett, 2000.

Drum, David. Making the Chemotherapy Decision, 2nd ed. Los Angeles: Lowell House, 1998.

OTHER

American Cancer Society. Cancer Drugs. Cancer Resource Center. 2000. 27 May 2001. <http://www2.cancer.org/drug_reference/index.cfm?ct=1&language=english>.

American Cancer Society. Infections in Individuals with Cancer. Cancer Resource Center. 30 Sep. 1999. 27 May 2001. <http://www3.cancer.org/cancerinfo/load_cont.asp?ct=1&doc=12>.

MEDLINEplus Drug Information. U.S. National Library of Medicine. 24 Jan. 2001. 22 May 2001. <http://www.nlm.nih.gov/medlineplus/druginfo/>.

Margaret Alic, Ph.D.

KEY TERMS

Gram-negative

Types of bacteria that do not retain Gram stain.

Gram-positive

Types of bacteria that retain Gram stain.

Mycobacteria

Rod-shaped bacteria, some of which cause human diseases such as tuberculosis.

Pneumocystis carinii

pneumonia (PCP) Serious type of pneumonia caused by the protozoan Pneumocystis carinii.

Protozoa

Single-celled animals.

Toxoplasmosis

Infection caused by the protozoan parasite Toxoplasma gondii, affecting animals and humans with suppressed immune systems.

Trichomoniasis

Infection caused by a protozoan of the genus Trichomonas ; especially vaginitis caused by Trichomonas vaginalis

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Antibiotic

Antibiotic

Antibiotics are chemical substances that can inhibit the growth of, and even destroy, harmful microorganisms. They are derived from special microorganisms or other living systems, and are produced on an industrial scale using a fermentation process. Although the principles of antibiotic action were not discovered until the twentieth century, the first known use of antibiotics was by the Chinese over 2,500 years ago. Today, over 10,000 antibiotic substances have been reported. Currently, antibiotics represent a multibillion dollar industry that continues to grow each year.

Background

Antibiotics are used in many forms—each of which imposes somewhat different manufacturing requirements. For bacterial infections on the skin surface, eye, or ear, an antibiotic may be applied as an ointment or cream. If the infection is internal, the antibiotic can be swallowed or injected directly into the body. In these cases, the antibiotic is delivered throughout the body by absorption into the bloodstream.

Antibiotics differ chemically so it is under-standable that they also differ in the types of infections they cure and the ways in which they cure them. Certain antibiotics destroy bacteria by affecting the structure of their cells. This can occur in one of two ways. First, the antibiotic can weaken the cell walls of the infectious bacteria, which causes them to burst. Second, antibiotics can cause the contents of the bacterial cells to leak out by damaging the cell membranes. Another way in which antibiotics function is by interfering with the bacteria's metabolism. Some antibiotics such as tetracycline and erythromycin interfere with protein synthesis. Antibiotics like rifampin inhibit nucleic acid biosynthesis. Still other antibiotics, such as sulfonamide or trimethoprim have a general blocking effect on cell metabolism.

The commercial development of an antibiotic is a long and costly proposal. It begins with basic research designed to identify organisms, which produce antibiotic compounds. During this phase, thousands of species are screened for any sign of antibacterial action. When one is found, the species is tested against a variety of known infectious bacteria. If the results are promising, the organism is grown on a large scale so the compound responsible for the antibiotic effect can be isolated. This is a complex procedure because thousands of antibiotic materials have already been discovered. Often, scientists find that their new antibiotics are not unique. If the material passes this phase, further testing can be done. This typically involves clinical testing to prove that the antibiotic works in animals and humans and is not harmful. If these tests are passed, the Food and Drug Administration (FDA) must then approve the antibiotic as a new drug. This whole process can take many years.

The large-scale production of an antibiotic depends on a fermentation process. During fermentation, large amounts of the antibiotic-producing organism are grown. During fermentation, the organisms produce the antibiotic material, which can then be isolated for use as a drug. For a new antibiotic to be economically feasible, manufacturers must be able to get a high yield of drug from the fermentation process, and be able to easily isolate it. Extensive research is usually required before a new antibiotic can be commercially scaled up.

History

While our scientific knowledge of antibiotics has only recently been developed, the practical application of antibiotics has existed for centuries. The first known use was by the Chinese about 2,500 years ago. During this time, they discovered that applying the moldy curd of soybeans to infections had certain therapeutic benefits. It was so effective that it became a standard treatment. Evidence suggests that other cultures used antibiotic-type substances as therapeutic agents. The Sudanese-Nubian civilization used a type of tetracycline antibiotic as early as 350 a.d. In Europe during the Middle Ages, crude plant extracts and cheese curds were also used to fight infection. Although these cultures used antibiotics, the general principles of antibiotic action were not understood until the twentieth century.

The development of modern antibiotics depended on a few key individuals who demonstrated to the world that materials derived from microorganisms could be used to cure infectious diseases. One of the first pioneers in this field was Louis Pasteur. In 1877, he and an associate discovered that the growth of disease-causing anthrax bacteria could be inhibited by a saprophytic bacteria. They showed that large amounts of anthrax bacilli could be given to animals with no adverse affects as long as the saprophytic bacilli were also given. Over the next few years, other observations supported the fact that some bacterially derived materials could prevent the growth of disease-causing bacteria.

In 1928, Alexander Fleming made one of the most important contributions to the field of antibiotics. In an experiment, he found that a strain of green Penicillium mold inhibited the growth of bacteria on an agar plate. This led to the development of the first modern era antibiotic, penicillin. A few years later in 1932, a paper was published which suggested a method for treating infected wounds using a penicillin preparation. Although these early samples of penicillin were functional, they were not reliable and further refinements were needed. These improvements came in the early 1940s when Howard Florey and associates discovered a new strain of Penicillium, which produced high yields of penicillin. This allowed large-scale production of penicillin, which helped launch the modern antibiotics industry.

After the discovery of penicillin, other antibiotics were sought. In 1939, work began on the isolation of potential antibiotic products from the soil bacteria streptomyces. It was around this time that the term antibiotic was introduced. Selman Waxman and associates discovered streptomycin in 1944. Subsequent studies resulted in the discovery of a host of new, different antibiotics including actinomycin, streptothricin, and neomycin all produced by Streptomyces. Other antibiotics that have been discovered since include bacitracin, polymyxin, viomycin, chloramphenicol and tetracyclines. Since the 1970s, most new antibiotics have been synthetic modifications of naturally occurring antibiotics.

Raw Materials

The compounds that make the fermentation broth are the primary raw materials required for antibiotic production. This broth is an aqueous solution made up of all of the ingredients necessary for the proliferation of the microorganisms. Typically, it contains a carbon source like molasses, or soy meal, both of which are made up of lactose and glucose sugars. These materials are needed as a food source for the organisms. Nitrogen is another necessary compound in the metabolic cycles of the organisms. For this reason, an ammonia salt is typically used. Additionally, trace elements needed for the proper growth of the antibiotic-producing organisms are included. These are components such as phosphorus, sulfur, magnesium, zinc, iron, and copper introduced through water soluble salts. To prevent foaming during fermentation, anti-foaming agents such as lard oil, octadecanol, and silicones are used.

The Manufacturing
Process

Although most antibiotics occur in nature, they are not normally available in the quantities necessary for large-scale production. For this reason, a fermentation process was developed. It involves isolating a desired microorganism, fueling growth of the culture and refining and isolating the final antibiotic product. It is important that sterile conditions be maintained throughout the manufacturing process, because contamination by foreign microbes will ruin the fermentation.

Starting the culture

  • 1 Before fermentation can begin, the desired antibiotic-producing organism must be isolated and its numbers must be increased by many times. To do this, a starter culture from a sample of previously isolated, cold-stored organisms is created in the lab. In order to grow the initial culture, a sample of the organism is transferred to an agar-containing plate. The initial culture is then put into shake flasks along with food and other nutrients necessary for growth. This creates a suspension, which can be transferred to seed tanks for further growth.
  • 2 The seed tanks are steel tanks designed to provide an ideal environment for growing microorganisms. They are filled with the all the things the specific microorganism would need to survive and thrive, including warm water and carbohydrate foods like lactose or glucose sugars. Additionally, they contain other necessary carbon sources, such as acetic acid, alcohols, or hydrocarbons, and nitrogen sources like ammonia salts. Growth factors like vitamins, amino acids, and minor nutrients round out the composition of the seed tank contents. The seed tanks are equipped with mixers, which keep the growth medium moving, and a pump to deliver sterilized, filtered air. After about 24-28 hours, the material in the seed tanks is transferred to the primary fermentation tanks.

Fermentation

  • 3 The fermentation tank is essentially a larger version of the steel, seed tank, which is able to hold about 30,000 gallons. It is filled with the same growth media found in the seed tank and also provides an environment inducive to growth. Here the microorganisms are allowed to grow and multiply. During this process, they excrete large quantities of the desired antibiotic. The tanks are cooled to keep the temperature between 73-81° F (23-27.2 ° C). It is constantly agitated, and a continuous stream of sterilized air is pumped into it. For this reason, anti-foaming agents are periodically added. Since pH control is vital for optimal growth, acids or bases are added to the tank as necessary.

Isolation and purification

  • 4 After three to five days, the maximum amount of antibiotic will have been produced and the isolation process can begin. Depending on the specific antibiotic produced, the fermentation broth is processed by various purification methods. For example, for antibiotic compounds that are water soluble, an ion-exchange method may be used for purification. In this method, the compound is first separated from the waste organic materials in the broth and then sent through equipment, which separates the other water-soluble compounds from the desired one. To isolate an oil-soluble antibiotic such as penicillin, a solvent extraction method is used. In this method, the broth is treated with organic solvents such as butyl acetate or methyl isobutyl ketone, which can specifically dissolve the antibiotic. The dissolved antibiotic is then recovered using various organic chemical means. At the end of this step, the manufacturer is typically left with a purified powdered form of the antibiotic, which can be further refined into different product types.

Refining

  • 5 Antibiotic products can take on many different forms. They can be sold in solutions for intravenous bags or syringes, in pill or gel capsule form, or they may be sold as powders, which are incorporated into topical ointments. Depending on the final form of the antibiotic, various refining steps may be taken after the initial isolation. For intravenous bags, the crystalline antibiotic can be dissolved in a solution, put in the bag, which is then hermetically sealed. For gel capsules, the powdered antibiotic is physically filled into the bottom half of a capsule then the top half is mechanically put in place. When used in topical ointments, the antibiotic is mixed into the ointment.
  • 6 From this point, the antibiotic product is transported to the final packaging stations. Here, the products are stacked and put in boxes. They are loaded up on trucks and transported to various distributors, hospitals, and pharmacies. The entire process of fermentation, recovery, and processing can take anywhere from five to eight days.

Quality Control

Quality control is of utmost importance in the production of antibiotics. Since it involves a fermentation process, steps must be taken to ensure that absolutely no contamination is introduced at any point during production. To this end, the medium and all of the processing equipment are thoroughly steam sterilized. During manufacturing, the quality of all the compounds is checked on a regular basis. Of particular importance are frequent checks of the condition of the microorganism culture during fermentation. These are accomplished using various chromatography techniques. Also, various physical and chemical properties of the finished product are checked such as pH, melting point, and moisture content.

In the United States, antibiotic production is highly regulated by the Food and Drug Administration (FDA). Depending on the application and type of antibiotic, more or less testing must be completed. For example, the FDA requires that for certain antibiotics each batch must be checked by them for effectiveness and purity. Only after they have certified the batch can it be sold for general consumption.

The Future

Since the development of a new drug is a costly proposition, pharmaceutical companies have done very little research in the last decade. However, an alarming development has spurred a revived interest in the development of new antibiotics. It turns out that some of the disease-causing bacteria have mutated and developed a resistance to many of the standard antibiotics. This could have grave consequences on the world's public health unless new antibiotics are discovered or improvements are made on the ones that are available. This challenging problem will be the focus of research for many years to come.

Where to Learn More

Books

Crueger, W. Biotechnology: A Textbook of Industrial Microbiology. Sunderland: Sinauer Associates, Inc., 1989.

Kirk Othmer Encyclopedia of Chemical Technology. New York: John Wiley & Sons, 1992.

Periodicals

Morell, Virginia. "Antibiotic Resistance: Road of No Return." Science 278 (October 24, 1997): 575-576.

Stinson, Stephen. "Drug Firms Restock Antibacterial Arsenal." Chemical & Engineering News (September 23,1996): 75-100.

PerryRomanowski

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Antibiotics

Antibiotics

Definition

Antibiotics are used for treatment or prevention of bacterial infection. They may be informally defined as the subgroup of anti-infectives that are derived from bacterial sources and are used to treat bacterial infections. Other classes of drugs, most notably the sulfonamides , may be effective antibacterials. Similarly, some antibiotics may have secondary uses, such as the use of demeclocycline (Declomycin, a tetracycline derivative) to treat the syndrome of inappropriate antidiuretic hormone (SIADH) secretion. Other antibiotics may be useful in treating protozoal infections.

Description

Classifications

Although there are several classification schemes for antibiotics, based on bacterial spectrum (broad versus narrow) or route of administration (injectable versus oral versus topical), or type of activity (bactericidal versus bacteriostatic), the most useful is based on chemical structure. Antibiotics within a structural class will generally show similar patterns of effectiveness, toxicity, and allergic potential.

PENICILLINS The penicillins are the oldest class of antibiotics and have a common chemical structure that they share with the cephalosporins. Classed as the betalactam antibiotics, the two groups are generally bacteriocidal, which means that they kill bacteria rather than simply inhibit its growth. The penicillins can be further subdivided. The natural penicillins are based on the original penicillin G structure; penicillinase-resistant penicillins, notably methicillin and oxacillin, are active even in the presence of the bacterial enzyme that inactivates most natural penicillins. Aminopenicillins such as ampicillin and amoxicillin have an extended spectrum of action compared with the natural penicillins; extended spectrum penicillins are effective against a wider range of bacteria. These generally include coverage for Pseudomonas aeruginosa.

CEPHALOSPORINS Cephalosporins and the closely related cephamycins and carbapenems, like the penicillins, contain a beta-lactam chemical structure. Consequently, there are patterns of cross-resistance and cross-allergenicity among the drugs in these classes. The "cepha" drugs are among the most diverse classes of antibiotics and are themselves subdivided into first, second, and third generations. Each generation has a broader spectrum of activity than the one before. In addition, cefoxitin, a cephamycin, is highly active against anaerobic bacteria, which offers utility in treatment of abdominal infections. The third generation drugs, cefotaxime, ceftizoxime, ceftriaxone, and others, cross the blood-brain barrier and may be used to treat meningitis and encephalitis . Cephalosporins are the usually preferred agents for surgical prophylaxis.

fluoroquinolones The fluoroquinolones are synthetic antibacterial agents and not derived from bacteria. They are included here because they can be readily interchanged with traditional antibiotics. An earlier, related class of antibacterial agents, the quinolones, drugs that were not well absorbed, could be used only to treat urinary tract infections. The fluoroquinolones, which are based on the older group, are broad-spectrum bacteriocidal drugs that are chemically unrelated to the penicillins or the cephalosporins. They are well distributed into bone tissue and so well absorbed that in general they are as effective by the oral route as by intravenous infusion.

TETRACYCLINES Tetracyclines got their name from the fact that they share a chemical structure that has four rings. They are derived from a species of Streptomyces bacteria. Broad-spectrum bacteriostatic agents, the tetracyclines may be effective against a wide variety of microorganisms, including rickettsia and amoebic parasites.

macrolides The macrolide antibiotics are derived from Streptomyces bacteria. Erythromycin, the prototype of this class, has a spectrum and use similar to penicillin. Newer members of the group, azithromycin and clarithromycin, are particularly useful for their high level of lung penetration. Clarithromycin has been widely used to treat Helicobacter pylori infections, the cause of stomach ulcers.

OTHERS Other classes of antibiotics include the aminoglycosides, which are particularly useful for their effectiveness in treating Pseudomonas aeruginosa infections, and the lincosamide drugs clindamycin and lincomycin, which are highly active against anaerobic pathogens. There are other, individual drugs which may have utility in specific infections.

General use

Antibiotics are used for treatment or prevention of bacterial infections. In most cases, they are prescribed for a short period of time to treat a specific infection. This period may range from three days to 10 days or more. More serious infections may require longer periods of treatment, up to several months or longer. Lower doses may be used over a long period of time to prevent the return of a serious infection.

Precautions

All antibiotics should be used as prescribed. These drugs will degrade over time and lose their potency. Not completing a prescribed course of treatment increases the probability that drug-resistant strains of organisms will develop.

Side effects

All antibiotics cause risk of overgrowth by non-susceptible bacteria. Manufacturers list other major hazards by class; however, the healthcare provider should review each drug individually to assess the degree of risk. Generally, breastfeeding may be continued while taking antibiotics, but nursing mothers should always check with their physician first. Excessive or inappropriate use may promote growth of resistant pathogens.

Hypersensitivity to penicillins may be common, and cross allergenicity with cephalosporins has been reported. (That is, those who are allergic to penicillin may also be allergic to cephalosporins.) Penicillins are classed as category B during pregnancy.

Several cephalosporins and related compounds have been associated with seizures. Cefmetazole, cefoperazone, cefotetan, and ceftriaxone may be associated with problems in poor blood clotting. Pseudomembranous colitis (an intestinal disorder) has been reported with cephalosporins and other broad spectrum antibiotics. Some drugs in this class may cause kidney toxicity. Cephalosporins are classed as category B during pregnancy.

Regarding fluoroquinolones, lomefloxacin has been associated with increased sensitivity to light. All drugs in this class have been associated with convulsions. Fluoroquinolones are classed as category C during pregnancy.

Of the tetracyclines, demeclocycline may cause increased photosensitivity. Minocycline may cause dizziness . Healthcare providers do not prescribe tetracyclines in children under the age of eight, and they specifically avoid doing so during periods of tooth development. Oral tetracyclines bind to anions such as calcium and iron. Although doxycycline and minocycline may be taken with meals, people must be advised to take other tetracycline antibiotics on an empty stomach and not to take the drugs with milk or other calcium-rich foods. Expired tetracycline should never be administered. These drugs have a pregnancy category D. Use during pregnancy may cause alterations in fetal bone development.

Of the macrolides, erythromycin may aggravate the weakness of people with myasthenia gravis. Azithromycin has, rarely, been associated with allergic reactions, including angioedema (swelling), anaphylaxis, and severe skin reactions. Oral erythromycin may be highly irritating to the stomach and when given by injection may cause severe phlebitis (inflammation of the veins). These drugs should be used with caution in people with liver dysfunction. Azithromycin and erythromycin are pregnancy category B. Clarithromycin, dirithromycin, and troleandomycin are pregnancy category C.

The aminoglycosides class of drugs causes kidney and ear problems. These problems can occur even with normal doses. Dosing should be based on kidney function, with periodic testing of both kidney function and hearing. These drugs are pregnancy category D.

Parental concerns

Parents should be sure to follow all dosage and label directions. This includes using all of a prescription at the time it is prescribed. Parents should also ensure that children cannot ingest any prescription medications by accident.

KEY TERMS

Bacteria Singular, bacterium; tiny, one-celled forms of life that cause many diseases and infections.

Bacterial spectrum The number of bacteria an antibiotic is effective against. Broad-spectrum antibiotics treat many different kinds of bacteria. Narrow-spectrum antibiotics treat fewer kinds.

Inflammation Pain, redness, swelling, and heat that develop in response to tissue irritation or injury. It usually is caused by the immune system's response to the body's contact with a foreign substance, such as an allergen or pathogen.

Meningitis An infection or inflammation of the membranes that cover the brain and spinal cord. It is usually caused by bacteria or a virus.

Microorganism An organism that is too small to be seen with the naked eye, such as a bacterium, virus, or fungus.

Organism A single, independent unit of life, such as a bacterium, a plant, or an animal.

Pregnancy category A system of classifying drugs according to their established risks for use during pregnancy. Category A: Controlled human studies have demonstrated no fetal risk. Category B: Animal studies indicate no fetal risk, but no human studies, or adverse effects in animals, but not in well-controlled human studies. Category C: No adequate human or animal studies, or adverse fetal effects in animal studies, but no available human data. Category D: Evidence of fetal risk, but benefits outweigh risks. Category X: Evidence of fetal risk. Risks outweigh any benefits.

Resources

BOOKS

Antibiotics: A Medical Dictionary, Bibliography, and Annotated Research Guide to Internet References. San Diego, CA: ICON Health Publications, 2003.

Archer, Gordon, and Ronald E. Polk. "Treatment and Prophylaxis of Bacterial Infections." In Harrison's Principles of Internal Medicine, 15th ed. Edited by Eugene Braunwald, et al. New York: McGraw-Hill, 2001, pp. 867-81.

Diasio, Robert B. "Principles of Drug Therapy." In Cecil Textbook of Medicine, 22nd ed. Edited by Lee Goldman, et al. Philadelphia: Saunders, 2003, pp. 124-34.

Scott, Geoffrey M. Handbook of Essential Antibiotics. New York: Gordon & Breach Publishing Group, 2004.

Sherman, Josepha. War against Germs. New York: Rosen Publishing Group, 2004.

PERIODICALS

Ashworth, M., et al. "Why has antibiotic prescribing for respiratory illness declined in primary care?" Journal of Public Health (Oxford) 26, no. 3 (2004): 26874.

Carrat, F., et al. "Antibiotic treatment for influenza does not affect resolution of illness, secondary visits or lost workdays." European Journal of Epidemiology 19, no. 7 (2004): 703-5.

Dancer, S. J. "How antibiotics can make us sick: the less obvious adverse effects of antimicrobial chemotherapy." Lancet Infectious Diseases 4, no. 10 (2004): 6119.

Simoes, J. A., et al. "Antibiotic resistance patterns of group B streptococcal clinical isolates." Infectious Diseases in Obstetrics and Gynecology 12, no. 1 (2004): 18.

ORGANIZATIONS

American Academy of Family Physicians. 11400 Tomahawk Creek Parkway, Leawood, KS 66211-2672. Web site: <www.aafp.org/>.

American Academy of Pediatrics. 141 Northwest Point Blvd., Elk Grove Village, IL 60007-1098. Web site: <www.aap.org/>.

American College of Emergency Physicians. PO Box 619911, Dallas, TX 75261-9911. Web site: <www.acep.org/>.

WEB SITES

"Antibiotic Guide." Johns Hopkins Point of Care Information Technology. Available online at <http://hopkinsabxguide.org/> (accessed December 19, 2004).

"Antibiotics: When They Can and Can't Help." American Academy of Family Physicians. Available online at <http://familydoctor.org/x2250.xml> (accessed December 19, 2004).

L. Fleming Fallon, Jr., MD, DrPH

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Fallon, L.. "Antibiotics." Gale Encyclopedia of Children's Health: Infancy through Adolescence. 2006. Encyclopedia.com. 25 Sep. 2016 <http://www.encyclopedia.com>.

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Antibiotics

Antibiotics

Definition

Antibiotics may be informally defined as the subgroup of anti-infectives derived from bacterial sources and used to treat bacterial infections.


Purpose

Antibiotics are used for treatment or prevention of bacterial infection. Other classes of drugs, most notably the sulfonamides , may be effective antibacterials. Similarly, some antibiotics may have secondary uses, such as the use of demeclocycline (Declomycin, a tetracycline derivative) to treat the syndrome of inappropriate antidiuretic hormone (SIADH) secretion. Other antibiotics may be useful in treating protozoal infections.


Description

Although there are several classification schemes for antibiotics, based on bacterial spectrum (broad versus narrow), route of administration (injectable versus oral versus topical), or type of activity (bactericidal versus bacteriostatic), the most useful is based on chemical structure. Antibiotics within a structural class will generally show similar patterns of effectiveness, toxicity, and allergic potential.


Penicillins

The penicillins are the oldest class of antibiotics and have a common chemical structure that they share with the cephalosporins . The two groups are classed as the beta-lactam antibiotics, and are generally bacteriocidalthat is, they kill bacteria rather than inhibit growth. The penicillins can be further subdivided. The natural penicillins are based on the original penicillin G structure; penicillinase-resistant penicillins, notably methicillin and oxacillin, are active even in the presence of the bacterial enzyme that inactivates most natural penicillins. Aminopenicillins such as ampicillin and amoxicillin have an extended spectrum of action compared with the natural penicillins; extended spectrum penicillins are effective against a wider range of bacteria. These generally include coverage for Pseudomonas aeruginosa and may provide the penicillin in combination with a penicillinase inhibitor.

Cephalosporins

Cephalosporins and the closely related cephamycins and carbapenems, like the penicillins, contain a beta-lactam chemical structure. Consequently, there are patterns of cross-resistance and cross-allergenicity among the drugs in these classes. The "cepha" drugs are among the most diverse classes of antibiotics, and are themselves subgrouped into first, second, and third generations. Each generation has a broader spectrum of activity than the one before. In addition, cefoxitin (Mefoxin), a cephamycin, is highly active against anaerobic bacteria, which makes it useful in prevention and treatment of infections of the intestines. The third generation drugs, cefotaxime, ceftizoxime, ceftriaxone, and others, cross the blood-brain barrier and may be used to treat meningitis and encephalitis. Cephalosporins are the usually preferred agents for prevention of infection during surgery.


Fluroquinolones

The fluroquinolones are synthetic antibacterial agents, and are not derived from bacteria. They are included here because they can be readily interchanged with traditional antibiotics. An earlier, related class of antibacterial agents, the quinolones, were not well absorbed, and could be used only to treat urinary tract infections. The fluroquinolones, which are based on the older group, are broad-spectrum bactericidal drugs that are chemically unrelated to the penicillins or the cephalosporins. They are well distributed into bone tissue, and so well absorbed that in general they are as effective by the oral route as by intravenous infusion.


Tetracyclines

Tetracyclines got their name because they share a chemical structure having four rings. They are derived from a species of Streptomyces bacteria. Broad-spectrum bacteriostatic agents, the tetracyclines may be effective against a wide variety of microorganisms, including rickettsia and amebic parasites.


Macrolides

The macrolide antibiotics are derived from Streptomyces bacteria, and got their name because they all have a macrocyclic lactone chemical structure. Erythromycin, the prototype of this class, has a spectrum and use similar to penicillin. Newer members of the group, azithromycin and clarithyromycin, are particularly useful for their high level of lung penetration. Clarithromycin has been widely used to treat Helicobacter pylori infections, the cause of stomach ulcers. For people who are allergic to penicillin, erythromycin is a valuable alternative. But, unlike penicillin, erythromycin can be very irritating both to the stomach when given by mouth, or to veins when given by injection.


Other classes

Other classes of antibiotics include the aminoglycosides, which are particularly useful for their effectiveness in treating Pseudomonas aeruginosa infections, and the lincosamindes, clindamycin and lincomycin, which are highly active against anaerobic pathogens. In addition, other individual drugs are available that may have utility in specific infections.


Recommended dosage

Dosage varies with drug, route of administration, pathogen, site of infection, and severity. Additional considerations include renal (kidney) function, age of patient, and other factors. Patients should consult manufac turers' recommendations or ask their doctors.


Side effects

All antibiotics cause risk of overgrowth by non-susceptible bacteria. Manufacturers list other major hazards by class; however, the health care provider should review each drug individually to assess the degree of risk. Generally, breastfeeding is not recommended while taking antibiotics because of risk of alteration to infant's intestinal flora, and risk of masking infection in the infant. Excessive or inappropriate use may promote growth of resistant pathogens.

  • Penicillins. Hypersensitivity may be common, and cross allergenicity with cephalosporins has been reported. Penicillins are classed as category B during pregnancy.
  • Cephalosporins. Several cephalosporins and related compounds have been associated with seizures. Cefmetazole, cefoperazone, cefotetan and ceftriaxone may be associated with a fall in prothrombin activity and coagulation abnormalities. Pseudomembranous colitis (inflammation of the colon) has been reported with cephalosporins and other broad spectrum antibiotics. Some drugs in this class may cause renal toxicity. Pregnancy category B.
  • Fluoroquinolones. Lomefloxacin has been associated with increased photosensitivity. All drugs in this class have been associated with convulsions. Pregnancy category C.
  • Tetracyclines. Demeclocycline may cause increased photosensitivity. Minocycline may cause dizziness. Children under the age of eight should not use tetracyclines, and specifically during periods of tooth development. Oral tetracyclines bind to anions such as calcium and iron. Although doxycycline and minocycline may be taken with meals, patients are advised to take other tetracycline antibiotics on an empty stomach, and not to take the drugs with milk or other calcium-rich foods. Expired tetracycline should never be administered. Pregnancy category D; use during pregnancy may cause alterations in bone development.
  • Macrolides. Erythromycin may aggravate the weakness of patients with myasthenia gravis. Azithromycin has, rarely, been associated with allergic reactions, including angioedema, anaphylaxis, and dermatologic reactions, including Stevens-Johnson syndrome and toxic epidermal necrolysis. Oral erythromycin may be highly irritating to the stomach and may cause severe phlebitis (inflammation of the vein) when given by injection. These drugs should be used with caution in patients with liver dysfunction. Pregnancy category B: Azithromycin, erythromycin. Pregnancy category C: Clarithromycin, dirithromycin, troleandomycin.
  • Aminoglycosides. This class of drugs causes kidney and hearing problems. These problems can occur even with normal doses. Dosing should be based on renal function, with periodic testing of both kidney function and hearing. Pregnancy category D.

Interactions

Use of all antibiotics may temporarily reduce the effectiveness of birth control pills; alternative birth control methods should be used while taking these medications. Antacids should be avoided while on tetracyclines as the calcium can impair absorption of this antibiotic class. For this reason, tetracyclines should not be taken just before or after consuming foods rich in calcium or iron. Consult specialized references for additional interactions to specific antibiotics.


Recommended usage

To minimize risk of adverse reactions and development of resistant strains of bacteria, antibiotics should be restricted to use in cases where there is either known or a reasonable presumption of bacterial infection. The use of antibiotics in viral infections is to be avoided. Avoid use of fluroquinolones for trivial infections.

In severe infections, presumptive therapy with a broad-spectrum antibiotic such as a third generation cephalosporin may be appropriate. Treatment should be changed to a narrow spectrum agent as soon as the pathogen has been identified. After 48 hours of treatment, if there is clinical improvement, an oral antibiotic should be considered.

When the pathogen is known or suspected to be Pseudomonas, a suitable beta-lactam drug is often prescribed in combination with an aminoglycoside. A single agent cannot be relied upon for treatment of Pseudomonas. When the patient has renal insufficiency, azactam should be considered in place of the aminoglycoside.

In treatment of children with antibiotic suspensions, caregivers should be instructed in use of oral syringes or measuring teaspoons. Household teaspoons are not standardized and will give unreliable doses.


Resources

periodicals

Moellering, R. C., Jr. "Linezolid." Summaries for Patients. Annals of Internal Medicine 138 (January 21, 2003): I-44.

other

Alliance for the Prudent Use of Antibiotics. Consumer Information. <http://www.tufts.edu/med/apua/Patients/patient.html>.

"Using antibiotics sensibly." MayoClinic.com. February 6, 2002 [cited June 25, 2003]. <http://www.mayoclinic.com/invoke.cfm?id=FL00075>.


Samuel Uretsky, PharmD

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Uretsky, Samuel. "Antibiotics." Gale Encyclopedia of Surgery: A Guide for Patients and Caregivers. 2004. Encyclopedia.com. 25 Sep. 2016 <http://www.encyclopedia.com>.

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Antibiotics

Antibiotics

Definition

Antibiotics may be informally defined as the subgroup of anti-infectives that are derived from bacterial sources and are used to treat bacterial infections. Other classes of drugs, most notably the sulfonamides, may be effective antibacterials. Similarly, some antibiotics may have secondary uses, such as the use of demeclocycline (Declomycin, a tetracycline derivative) to treat the syndrome of inappropriate antidiuretic hormone (SIADH) secretion. Other antibiotics may be useful in treating protozoal infections.

Purpose

Antibiotics are used for treatment or prevention of bacterial infection.

Description

Classifications

Although there are several classification schemes for antibiotics, based on bacterial spectrum (broad versus narrow) or route of administration (injectable versus oral versus topical), or type of activity (bactericidal vs. bacteriostatic), the most useful is based on chemical structure. Antibiotics within a structural class will generally show similar patterns of effectiveness, toxicity, and allergic potential.

PENICILLINS. The penicillins are the oldest class of antibiotics, and have a common chemical structure which they share with the cephalopsorins. The two groups are classed as the beta-lactam antibiotics, and are generally bacteriocidalthat is, they kill bacteria rather than inhibiting growth. The penicillins can be further subdivided. The natural pencillins are based on the original penicillin G structure; penicillinase-resistant penicillins, notably methicillin and oxacillin, are active even in the presence of the bacterial enzyme that inactivates most natural penicillins. Aminopenicillins such as ampicillin and amoxicillin have an extended spectrum of action compared with the natural penicillins; extended spectrum penicillins are effective against a wider range of bacteria. These generally include coverage for Pseudomonas aeruginaosa and may provide the penicillin in combination with a penicillinase inhibitor.

CEPHALOSPORINS. Cephalosporins and the closely related cephamycins and carbapenems, like the pencillins, contain a beta-lactam chemical structure. Consequently, there are patterns of cross-resistance and cross-allergenicity among the drugs in these classes. The "cepha" drugs are among the most diverse classes of antibiotics, and are themselves subgrouped into 1st, 2nd and 3rd generations. Each generation has a broader spectrum of activity than the one before. In addition, cefoxitin, a cephamycin, is highly active against anaerobic bacteria, which offers utility in treatment of abdominal infections. The 3rd generation drugs, cefotaxime, ceftizoxime, ceftriaxone and others, cross the blood-brain barrier and may be used to treat meningitis and encephalitis. Cephalopsorins are the usually preferred agents for surgical prophylaxis.

FLUROQUINOLONES. The fluroquinolones are synthetic antibacterial agents, and not derived from bacteria. They are included here because they can be readily interchanged with traditional antibiotics. An earlier, related class of antibacterial agents, the quinolones, were not well absorbed, and could be used only to treat urinary tract infections. The fluroquinolones, which are based on the older group, are broad-spectrum bacteriocidal drugs that are chemically unrelated to the penicillins or the cephaloprosins. They are well distributed into bone tissue, and so well absorbed that in general they are as effective by the oral route as by intravenous infusion.

TETRACYCLINES. Tetracyclines got their name because they share a chemical structure that has four rings. They are derived from a species of Streptomyces bacteria. Broad-spectrum bacteriostatic agents, the tetracyclines may be effective against a wide variety of microorganisms, including rickettsia and amoebic parasites.

MACROLIDES. The macrolide antibiotics are derived from Streptomyces bacteria, and got their name because they all have a macrocyclic lactone chemical structure. Erythromycin, the prototype of this class, has a spectrum and use similar to penicillin. Newer members of the group, azithromycin and clarithyromycin, are particularly useful for their high level of lung penetration. Clarithromycin has been widely used to treat Helicobacter pylori infections, the cause of stomach ulcers.

OTHERS. Other classes of antibiotics include the aminoglycosides, which are particularly useful for their effectiveness in treating Pseudomonas aeruginosa infections; the lincosamindes, clindamycin and lincomycin, which are highly active against anaerobic pathogens. There are other, individual drugs which may have utility in specific infections.

Recommended dosage

Dosage varies with drug, route of administration, pathogen, site of infection, and severity. Additional considerations include renal function, age of patient, and other factors. Consult manufacturers' recommendations for dose and route.

KEY TERMS

Bacteria Tiny, one-celled forms of life that cause many diseases and infections.

Inflammation Pain, redness, swelling, and heat that usually develop in response to injury or illness.

Meningitis Inflammation of tissues that surround the brain and spinal cord.

Microorganism An organism that is too small to be seen with the naked eye.

Organism A single, independent unit of life, such as a bacterium, a plant or an animal.

Pregnancy category A system of classifying drugs according to their established risks for use during pregnancy. Category A: Controlled human studies have demonstrated no fetal risk. Category B: Animal studies indicate no fetal risk, but no human studies; or adverse effects in animals, but not in well-controlled human studies. Category C: No adequate human or animal studies; or adverse fetal effects in animal studies, but no available human data. Category D: Evidence of fetal risk, but benefits outweigh risks. Category X: Evidence of fetal risk. Risks outweigh any benefits.

Side effects

All antibiotics cause risk of overgrowth by non-susceptible bacteria. Manufacturers list other major hazards by class; however, the health care provider should review each drug individually to assess the degree of risk. Generally, breastfeeding is not recommended while taking antibiotics because of risk of alteration to infant's intestinal flora, and risk of masking infection in the infant. Excessive or inappropriate use may promote growth of resistant pathogens.

Penicillins: Hypersensitivity may be common, and cross allergenicity with cephalosporins has been reported. Penicillins are classed as category B during pregnancy.

Cephalopsorins: Several cephalopsorins and related compounds have been associated with seizures. Cefmetazole, cefoperazone, cefotetan and ceftriaxone may be associated with a fall in prothrombin activity and coagulation abnormalities. Pseudomembranous colitis has been reported with cephalosporins and other broad spectrum antibiotics. Some drugs in this class may cause renal toxicity. Pregnancy category B.

Fluroquinolones: Lomefloxacin has been associated with increased photosensitivity. All drugs in this class have been associated with convulsions. Pregnancy category C.

Tetracyclines: Demeclocycline may cause increased photosensitivity. Minocycline may cause dizziness. Do not use tetracyclines in children under the age of eight, and specifically avoid during periods of tooth development. Oral tetracyclines bind to anions such as calcium and iron. Although doxycycline and minocycline may be taken with meals, patients must be advised to take other tetracycline antibiotics on an empty stomach, and not to take the drugs with milk or other calcium-rich foods. Expired tetracycline should never be administered. Pregnancy category D. Use during pregnancy may cause alterations in bone development.

Macrolides: Erythromycin may aggravate the weakness of patients with myasthenia gravis. Azithromycin has, rarely, been associated with allergic reactions, including angioedema, anaphylaxis, and dermatologic reactions, including Stevens-Johnson syndrome and toxic epidermal necrolysis. Oral erythromycin may be highly irritating to the stomach and when given by injection may cause severe phlebitis. These drugs should be used with caution in patients with liver dysfunction. Pregnancy category B: Azithromycin, erythromycin. Pregnancy category C: Clarithromycin, dirithromycin, troleandomycin.

Aminoglycosides: This class of drugs causes kidney and ototoxicity. These problems can occur even with normal doses. Dosing should be based on renal function, with periodic testing of both kidney function and hearing. Pregnancy category D.

Recommended usage

To minimize risk of adverse reactions and development of resistant strains of bacteria, antibiotics should be restricted to use in cases where there is either known or a reasonable presumption of bacterial infection. The use of antibiotics in viral infections is to be avoided. Avoid use of fluroquinolones for trivial infections.

In severe infections, presumptive therapy with a broad-spectrum antibiotic such as a 3rd generation cephalosporin may be appropriate. Treatment should be changed to a narrow spectrum agent as soon as the pathogen has been identified. After 48 hours of treatment, if there is clinical improvement, an oral antibiotic should be considered.

Resources

PERIODICALS

"Consumer Alert: Antibiotic Resistance Is Growing!" People's Medical Society Newsletter 16 (August 1997): 1.

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Antibiotics

Antibiotics

Antibiotics are medications taken to fight infections caused by bacteria. When they first became available during World War II (1939-1945), antibiotics were called "wonder drugs" because of their stunning record for safety and effectiveness. Well-known antibiotics include penicillin, streptomycin, and erythromycin. Antibiotics are usually taken orally (by mouth) or given as inoculations.

How Bacteria Make Us III

Bacteria are single-celled organisms that exist everywhere in nature and can have beneficial purposes. Most bacteria are harmless to humans. Disease may result, however, when an infectious type of bacteria enters the human body, by way of the nose or mouth or through a wound. Many types of bacteria reproduce by cell division (the one-celled organism divides into two identical organisms), a very rapid process that sometimes takes as little as 20 minutes. The chemicals bacteria release may be toxic (poisonous) to human cells or may interfere with cell function. Bacteria are responsible for such debilitating and even fatal human diseases as pneumonia, typhoid fever, Rocky Mountain Spotted Fever, and tuberculosis.

Antibiotic drugs are prepared from natural compounds that are antagonistic (harmful) to bacteria. Some fungi and benign (harmless) bacteria can defend themselves against harmful bacteria by producing chemicals that destroy bacterial cells. Scientists and researchers have created many effective drugs for human use out of such bacteria as mold in the Penicillium family or Streptomyces griseus. These anti (against) biotic (life) compounds usually work by either damaging the harmful bacteria's cell membrane (the thin layer of animal or plant tissue that covers an organ or bodyily fluid) or preventing its growth.

Fleming Discovers Penicillin

Scientists of the early 1800s first classified bacteria. In 1829 they established the name Bacterium as their genus (a grouping of species with common origins). Bacteriology was an experimental science that emerged slowly until a major breakthrough occurred in 1928 that led to the development of penicillin. Scottish doctor Sir Alexander Fleming (1881-1955; winner of the 1945 Nobel Prize in medicine with Howard Walter Florey and Ernst Boris Chain) was growing colorful patches of bacteria in covered dishes in his crowded St. Mary's Hospital Medical School laboratory. He noticed that a green mold had gotten into one of the dishes. Fleming knew that mold spores traveled through the air and could easily land and grow in any dish left uncovered. In this particular dish the bacteria closest to the green mold seemed to have disappeared or dissolved. Fleming examined the mold carefully and photographed it. An associate identified the growth as Penicillium notatum.

Curious about how the bacteria in this dish were killed, Fleming took the greenish "fluff in the dish and made a mixture that his laboratory workers called "mold juice." Fleming named the juice "penicillin" and gave it to some laboratory mice. He found that the penicillin killed only the harmful bacteria and not the healthy cells in the mice. This made Fleming's "mold juice" safer than any other known bacteria-killing substances. It was an incredible discovery. If this mold mixture could be made into a drug, then someone with an infection could be cured of disease without being harmed by the cure.Unfortunately, Fleming ran into difficulties turning penicillin into a drug because he was unable to purify and concentrate the substance.

Further Breakthroughs

The next breakthrough came in 1939 from scientists studying microorganisms in soil and how these organisms helped to keep soil healthy. In 1939 American soil microbiologist Selman Abraham Waksman (1888-1973; winner of the 1952 Nobel Prize for medicine) was analyzing the antibacterial properties of soil organisms. Working on streptomycetes fungi at Rutgers University laboratory in Newark, New Jersey, Waksman invented the term "antibiotic" to describe a compound that would harm bacteria without being toxic to human cells. He isolated (separated) antibacterial agents from the streptomycetes, but he found them all to be toxic to human cells.

In 1940 Florey (1898-1968; professor of pathology originally from Australia) and Chain (1906-1979; German biochemist who had fled Hitler's Germany) began to experiment with penicillin at Oxford University in England. After many experiments, the duo succeeded in purifying penicillin and began testing it on mice. When penicillin caused few side effects in the mice, Florey and Chain began testing it on humans. With the outbreak of World War II (1939-1945), wounded were crowding into hospitals. Florey and Chain's team of workers rushed to develop penicillin in large quantities to fight bacterial infections.

By 1942 penicillin was being mass produced by British pharmaceutical companies. Through the distribution of penicillin, many soldiers were saved from the infections that developed after they were wounded in battle. Penicillin also reduced the rate at which people died from bacterial pneumonia. Where once pneumonia killed 60 to 80 percent of the people who came down with the lung infection, penicillin lowered the rate to 1 to 5 percent.

Other Developments

Despite its effectiveness, penicillin did not cure every bacterial infection. Eventually scientists understood that the drug worked only against Gram-positive bacteria (a range of bacteria that reveal a blue stain in certain laboratory tests). During the early 1940s Waksman focused on Gramnegative bacteria (a range of bacteria that loses the blue stain). He eventually found a nontoxic compound derived from Streptomycetes griseus mold which he named "streptomycin." In January of 1944, he announced that this antibiotic could work against both Gram-positive and Gram-negative bacteria and was particularly effective against tuberculosis.

Initially made only from natural substances, antibiotics were soon formulated from synthetic (non-living) or partly synthetic materials. In 1945 Benjamin Dugger, Y. Subbarow, and A. Dormbush discovered aureomycin, the first of the class of antibiotics known as tetracyclines. John Ehrlich and Quentin Bartz isolated another soil microbe in 1947 that chemists at Parke Davis & Company found could be synthesized (made) into an antibiotic. The new drug, chloramphenicol (an antibiotic that is antagonistic, or harmful, to a wide spectrum of bacteria), became one of the first bestselling synthetic drugs. Other synthetic antibiotics include terramycin, erythromycin, and bacitracin.

Taking Antibiotics

Antibiotics may be injected with a needle and syringe or taken by mouth in pill or liquid form. They prevent bacterial cells from growing or dividing normally. For example, penicillin prevents bacteria from forming their cell walls. The compound in the antibiotic mimics (acts like) similar compounds in the bacterial cell wall. But when the antibiotic becomes part of the bacterial cell wall, it leaves a gap. The bacterium's cell contents are no longer properly encased and protected, so the contents spill out and the cell dies.

Resistant Bacteria

An antibiotic may be very effective in halting the reproduction of bacteria at first. There are always some bacteria, however, that are naturally resistant to the drug. Soon the resistant strain is able to catch up and reproduce in strong numbers. Antibiotic resistance was noticed as early as the 1940s. Some authorities believe that overuse of antibiotics causes bacteria to become resistant. One example of overuse is in factory farming of poultry and livestock, in which antibiotics are routinely administered to animals as a preventive medicine to keep them from getting sick. Eventually, the antibiotics may fail to work because the infection is caused by resistant bacteria.

The same phenomenon can be observed in humans. The U.S. Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia, reported in January of 1996 that deaths from infectious diseases are on the upswing. According to the report, death from infectious diseases rose 58 percent between 1980 and 1992. (In 1980 infectious diseases caused 41 out of every 100,000 deaths. In 1992 infection was responsible for 65 out of every 100,000 deaths.) The CDC claims that antibiotics have been over-prescribed and improperly prescribed, which results in resistant bacteria (bacteria exposed to, but not killed by, antibiotics can mutate to make themselves immune to antibiotics). The resistant bacteria can then pass their resistance to other bacteria. When the resistant microbes produce illness in humans, antibiotics that have traditionally cured that disease no longer work.

The CDC predicts the possibility of a post-antibiotic eraa time when antibiotics no longer workand advises that antibiotics be used very carefully and only according to directions. Furthermore, before prescribing antibiotics, health care providers should first take a sample of the bacteria (which is then grown in a culture). This allows the bacteria to be clearly identified and indicates exactly which antibiotic should be prescribed.

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Antibiotics

Antibiotics


Antibiotics are substances that inhibit the growth of microorganisms (anti-metabolites ) or their replication (a bacteriostatic effect). They were traditionally obtained by extracting them from cultures of microbes. However, most drugs on the market today are semisynthetic derivatives of natural products. Sulfa drugs, discovered in the 1930s, were the first antimicrobial agents put into clinical use. Unfortunately, many bacteria are not susceptible to sulfonamides , and with the outbreak of World War II came the need for other more potent antibacterial agents. The serendipitous discovery of penicillin is, without a doubt, the most celebrated breakthrough in the history of antibiotics. In the late 1920s, while working in a London hospital, Alexander Fleming observed a mold overtaking a culture of staphylococcus bacteria he was growing in his laboratory. He extracted juices from the mold and, in 1929, reported that the extract, which he called penicillin, had antiseptic (anti-infectious) activity. The fungus was subsequently identified as Penicillium notatum (now called Penicillium chrysogenum ). It was not until the 1940s that penicillin was put into clinical use. Howard W. Florey, professor of pathology at Oxford's Sir William Dunn School of Pathology, and Ernst B. Chain are credited with culturing the fungus and producing the first significant quantities of penicillin for treating bacterial infections. In 1945 Fleming, Florey, and Chain received the Nobel Prize in physiology or medicine "for the discovery of penicillin and its curative effect in various infectious diseases."

Extracts from microorganisms are still an important source of antibiotics today. Clinically, antibiotics are described as possessing either broad- or narrow-spectrum activity. Bacteria are classified based on a staining technique developed by Danish microbiologist Hans Christian Gram. The bacterial cell walls of gram-positive bacteria stain blue when treated with either crystal violet or methylene blue, while gram-negative bacteria do not retain the stain and appear red. Broad-spectrum antibiotics are capable of inhibiting both gram-positive and gram-negative bacterial cultures. Grampositive bacteria have simpler cell walls than gram-negative strains and are susceptible to less toxic, narrow-spectrum antibiotics.

β -Lactam Antibiotics

A variety of penicillins have been produced by the fermentation of Penicillium chrysogenum in the presence of different nutrients. Penicillin G (benzylpenicillin; see Figure 1) predominates when the culture medium is rich in phenylacetic acid, whereas the incorporation of phenoxyacetic acid favors penicillin V (phenoxymethylpenicillin). Semisynthetic penicillins, such as ampicillin and amoxicillin, are prepared by replacing the aromatic side chain of biosynthetically derived penicillins with other chemical groups. All penicillins are β -lactam (see Figure 2) antibiotics and have the same mechanism of action: They inhibit bacterial cell wall biosynthesis .

Bacterial cell walls differ from mammalian cell walls and are therefore attractive targets for antibiotics. Bacterial cell walls contain β -lactam receptors , known as penicillin-binding proteins (PBPs). β -Lactam antibiotics

bind to the PBPs of bacterial cell walls and prevent their growth and repair. Widespread use of penicillin, however, has led to drug resistance . Because microorganisms multiply rapidly, strains of bacteria with enzymes capable of hydrolyzing β -lactam rings (β -lactamases) have evolved. β -lactamases are capable of inactivating β -lactam antibiotics before they bind to receptors on cell walls. As a result, physicians sometimes prescribe β -lactamase inhibitors to patients on penicillin therapy to circumvent drug inactivation by bacterial enzymes.

The cephalosporins comprise another important class of broad-spectrum β -lactam antibiotics. Cephalosporins were originally isolated from cultures of Cephalosporium acremonium. Cephalexin (Keflex) is a semisynthetic cephalosporin frequently prescribed to treat ear and skin infections caused by staphylococci or streptococci.

Antibiotics That Inhibit Protein Synthesis

There are also a large number of antibiotics structurally unrelated to penicillins and cephalosporins. These compounds exert their antimicrobial activity by inhibiting protein biosynthesis. In 1947 chloramphenicol (see Figure 3) was isolated from cultures of Streptomyces venezuelae. It is a broad-spectrum bacteriostatic agent that interferes with protein synthesis by binding to bacterial ribosomes . The use of chloramphenicol in humans is limited because of the drug's toxicity. It inhibits liver enzymes and suppresses red blood cell formation.

Aminoglycosides are amino sugars with broad-spectrum antibiotic activity. Streptomycin , isolated from Streptomyces griseus, was the first aminoglycoside antibiotic discovered. Although streptomycin initially proved to be a potent agent against gram-negative bacteria, rapid microbial resistance to the drug has limited its use and today streptomycin is generally administered in combination with other antibiotics. Neomycin is a broad-spectrum aminoglycoside antibiotic isolated from Streptomyces fradiae. However, because of the adverse effects of neomycin on the kidneys and ear, its use in humans is restricted to topical applications, often in combination with other antibiotics or corticosteroids. Concerns over the potential risks associated with aminoglycoside therapy, chiefly nephrotoxicity (kidney disease) and ototoxicity (damage to the ear canal), have diminished their use.

In 1952 the broad-spectrum antibiotic erythromycin was isolated from cultures of Streptomyces erythreus (later renamed Saccharopolyspora erythraea ). The erythromycins are macrolide antibiotics that typically have a 12-, 14-, or 16-membered cyclic backbone which is a lactone (a cyclic ester ; see Figure 4).

Erythromycin A, the major fermentation component of S. erythraea, is a 14-membered ring macrolide that is used by medicinal chemists as the foundation for building semisynthetic derivatives of erythromycin antibiotics. (Macrolides inhibit bacteria by interfering with microbial protein biosynthesis.) Semisynthetic macrolides are popular with clinicians because they can be administered orally and have relatively low toxicity. They are often used to treat respiratory tract infections, and have been especially effective against conditions such as Legionnaires' disease and communityacquired pneumonia. Erythromycin therapy is often prescribed for individuals allergic to penicillin. One of the most widely used macrolide antibiotics

derived from erythromycin A is azithromycin (Zithromax). Resistance to macrolide antibiotics generally involves mutations of bacterial ribosomal RNA that prevent macrolide binding.

In the late 1940s and early 1950s a series of tetracycline antibiotics was isolated from cultures of streptomyces. All tetracyclines consist of four fused 6-membered rings (see Figure 5). Tetracyclines are broad-spectrum antibiotics that interfere with protein synthesis by binding to bacterial ribosomes. Unfortunately, the frequent use of tetracyclines to treat minor infections has led to resistance among previously susceptible strains of bacteria (pneumococci and staphylococci). Resistance to tetracyclines occurs when bacteria either develop proteins that prevent ribosomal binding by tetracyclines, or synthesize enzymes capable of inactivating tetracyclines.

Widespread use of antibiotics and rapid microbial evolution have led to highly resistant bacterial strains. Although most scientists no longer believe that a single drug will be developed to wipe out all infectious diseases, there is increasing demand for new antimicrobial agents. Currently, combined drug therapy appears to be the most effective means of circumventing microbial resistance to antibiotics.

see also Fleming, Alexander; Penicillin; Sulfa Drugs.

Nanette M. Wachter

Bibliography

American Chemical Society (2000). The Pharmaceutical Century: Ten Decades of Drug Discovery. Washington, DC: ACS Publications.

Katzung, Bertram G. (1998). Basic & Clinical Pharmacology, 7th edition. Stamford, CT: Appleton & Lange.

Williams, David A., and Lemke, Thomas L. (2002). Foye's Principles of Medicinal Chemistry, 5th edition. Baltimore, MD: Lippincott Williams & Wilkins.

Wolff, Manfred E., ed. (1996). Burger's Medicinal Chemistry and Drug Discovery, 5th edition. New York: Wiley.

Internet Resources

"The Nobel Prize in Physiology or Medicine 1945." Nobel Foundation E-Museum. Available from <http://www.nobel.se>.

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Antibiotic-Associated Colitis

Antibiotic-Associated Colitis

Definition

Antibiotic-associated colitis is an inflammation of the intestines that sometimes occurs following antibiotic treatment and is caused by toxins produced by the bacterium Clostridium difficile.

Description

Antibiotic-associated colitis, also called antibiotic-associated enterocolitis, can occur following antibiotic treatment. The bacteria Clostridia difficile are normally found in the intestines of 5% of healthy adults, but people can also pick up the bacteria while they are in a hospital or nursing home. In a healthy person, harmless resident intestinal bacteria compete with each other for food and places to "sit" along the inner intestinal wall. When antibiotics are given, most of the resident bacteria are killed. With fewer bacteria to compete with, the normally harmless Clostridia difficile grow rapidly and produce toxins. These toxins damage the inner wall of the intestines and cause inflammation and diarrhea.

Although all antibiotics can cause this disease, it is most commonly caused by clindamycin (Cleocin), ampicillin (Omnipen), amoxicillin (Amoxil, Augmentin, or Wymox), and any in the cephalosporin class (such as cefazolin or cephalexin). Symptoms of the condition can occur during antibiotic treatment or within four weeks after the treatment has stopped.

In approximately half of cases of antibiotic-associated colitis, the condition progresses to a more severe form of colitis called pseudomembranous enterocolitis in which pseudomembranes are excreted in the stools. Pseudomembranes are membrane-like collections of white blood cells, mucus, and the protein that causes blood to clot (fibrin) that are released by the damaged intestinal wall.

Causes and symptoms

Antibiotic-associated colitis is caused by toxins produced by the bacterium Clostridium difficile after treatment with antibiotics. When most of the other intestinal bacteria have been killed, Clostridium difficile grows rapidly and releases toxins that damage the intestinal wall. The disease and symptoms are caused by these toxins, not by the bacterium itself.

Symptoms of antibiotic-associated colitis usually begin four to ten days after antibiotic treatment has begun. The early signs and symptoms of this disease include lower abdominal cramps, an increased need to pass stool, and watery diarrhea. As the disease progresses, the patient may experience a general ill feeling, fatigue, abdominal pain, and fever. If the disease proceeds to pseudomembranous enterocolitis, the patient may also experience nausea, vomiting, large amounts of watery diarrhea, and a very high fever (104-105°F/40-40.5°C). Complications of antibiotic-associated colitis include severe dehydration, imbalances in blood minerals, low blood pressure, fluid accumulation in deep skin (edema ), enlargement of the large intestine (toxic megacolon), and the formation of a tear (perforation) in the wall of the large intestine.

The Clostridium difficile toxin is found in the stools of persons older than 60 years of age 20-100 times more frequently than in the stools of persons who are 10-20 years old. As a result, the elderly are much more prone to developing antibiotic-associated colitis than younger individuals.

Diagnosis

Antibiotic-associated colitis can be diagnosed by the symptoms and recent medical history of the patient, by a laboratory test for the bacterial toxin, and/or by using a procedure called endoscopy.

KEY TERMS

Colitis Inflammation of the colon.

Edema Fluid accumulation in a tissue.

Endoscopy A procedure in which a thin, lighted instrument is inserted into the interior of a hollow organ, such as the rectum and used to visually inspect the inner intestinal lining.

Fibrin A fibrous blood protein vital to coagulation and blood clot formation.

Rectum The last part of the intestine. Stool passes through the rectum and out through the anal opening.

Toxic megacolon Acute enlargement or dilation of the large intestine.

If the diarrhea and related symptoms occurred after the patient received antibiotics, antibiotic-associated colitis may be suspected. A stool sample may be analyzed for the presence of the Clostridium difficile toxin. This toxin test is the preferred diagnostic test for antibiotic-associated colitis. One frequently used test for the toxin involves adding the processed stool sample to a human cell culture. If the toxin is present in the stool sample, the cells die. It may take up to two days to get the results from this test. A simpler test, which provides results in two to three hours, is also available. Symptoms and toxin test results are usually enough to diagnose the disease.

Another tool that may be useful in the diagnosis of antibiotic-associated colitis, however, is a procedure called an endoscopy that involves inserting a thin, lighted tube into the rectum to visually inspect the intestinal lining. Two different types of endoscopy procedures, the sigmoidoscopy and the colonoscopy, are used to view different parts of the large intestine. These procedures are performed in a hospital or doctor's office. Patients are sedated during the procedure to make them more comfortable and are allowed to go home after recovering from the sedation.

Treatment

Diarrhea, regardless of the cause, is always treated by encouraging the individual to replace lost fluids and prevent dehydration. One method to treat antibiotic-associated colitis is to simply stop taking the antibiotic that caused the disease. This allows the normal intestinal bacteria to repopulate the intestines and inhibits the overgrowth of Clostridium difficile. Many patients with mild disease respond well to this and are free from diarrhea within two weeks. It is important, however, to make sure that the original disease for which the antibiotics were prescribed is treated.

Because of the potential seriousness of this disease, most patients are given another antibiotic to control the growth of the Clostridium difficile, usually vancomycin (Vancocin) or metronidazole (Flagyl or Protostat). Both are designed to be taken orally four times a day for 10-14 days. Upon finishing antibiotic treatment, approximately 15-20% of patients will experience a relapse of diarrhea within one to five weeks. Mild relapses can go untreated with great success, however, severe relapses of diarrhea require another round of antibiotic treatment. Instead of further antibiotic treatment, a cholestyramine resin (Questran or Prevalite) may be given. The bacterial toxins produced in the intestine stick to the resin and are passed out with the resin in the stool. Unfortunately, however, vancomycin also sticks to the resin, so these two drugs cannot be taken at the same time. Serious disease may require hospitalization so that the patient can be monitored, treated, and rehydrated.

Alternative treatment

The goal of alternative treatment for antibiotic-associated enterocolitis is to repopulate the intestinal environment with microorganisms that are normal and healthy for the intestinal tract. These microorgansisms then compete for space and keep the Clostridium difficile from over-populating.

Several types of supplements can be used. Supplements containing Lactobacillus acidophilus, the bacteria commonly found in yogurt and some types of milk, Lactobacillus bifidus, and Streptococcus faecium, are available in many stores in powder, capsule, tablet, and liquid form. Acidophilus also acts as a mild antibiotic, which helps it to reestablish itself in the intestine, and all may aid in the production of some B vitamins and vitamin K. These supplements can be taken individually and alternated weekly or together following one or more courses of antibiotics.

Prognosis

With appropriate treatment and replenishment of fluids, the prognosis is generally excellent. One or more relapses can occur. Very severe colitis can cause a tear (perforation) in the wall of the large intestine that would require major surgery. Perforation of the intestine can cause a serious abdominal infection. Antibiotic-associated colitis can be fatal in people who are elderly and/or have a serious underlying illness, such as cancer.

Prevention

There are no specific preventative measures for this disease. Good general health can reduce the chance of developing a bacterial infection that would require antibiotic treatment and the chance of picking up the Clostridia bacteria. Maintaining good general health can also reduce the seriousness and length of the condition, should it develop following antibiotic therapy.

Resources

OTHER

Mayo Clinic Online. March 5, 1998. http://www.mayohealth.org.

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Antibiotics

Antibiotics

The discovery of antibiotics greatly improved the quality of human life in the twentieth century. Antibiotics are drugs such as penicillin (pronounced pen-ih-SILL-in) and streptomycin (pronounced strep-toe-MY-sin) used to fight infections and infectious diseases caused by bacteria. Antibiotic drugs are made from living organisms such as fungi, molds, and certain soil bacteria that are harmful to disease-causing bacteria. Antibiotics can also be produced synthetically (artificially) or combined with natural substances to form semisynthetic antibiotics. These compounds work against strains of bacteria that are resistant to other antibiotics.

Some microscopic bacteria that enter the human body through an opening or a wound find abundant food and reproduce quickly in great numbers, releasing toxins (poisons) as they grow or when they die. The toxins can destroy human cells or interfere with cell function, causing diseases like pneumonia or tuberculosis. Antibiotics fight bacteria either by killing them or by preventing them from multiplying. (Indeed, the word antibiotic comes from anti-, meaning "against," and bios, meaning "life.") It is believed that antibiotics accomplish these actions by damaging bacterial cell walls or by otherwise interfering with the function of the cells.

History of antibiotics

Sulfa drugs. Sulfa drugs, originally developed for use in the dye industry, were the first effective drugs used to fight bacterial infection in humans. Prontosil, the first sulfa drug, was discovered in 1935 by German chemist Gerhard Domagk (18951964). Also called sulfonamides (pronounced sul-FOHN-uh-midze), these drugs are synthesized (made) in the laboratory from a crystalline compound called sulfanilamide (pronounced sul-fuh-NILL-uh-mide). They work by blocking the growth and multiplication of bacteria and were initially effective against a broad range of bacteria. However, many strains of bacteria have developed a resistance to sulfa drugs. Resistance occurs when some bacteria survive attack by the antibacterial drug and change in such a way that they are no longer affected by the drug's action.

Sulfa drugs are most commonly used today in the treatment of urinary tract infections. The drugs are usually taken by mouth, but other forms include creams that can be applied to burn wounds to prevent infection and ointments and drops used for eye infections.

Words to Know

Antibacterial: Working against bacteria either by destroying it or keeping it from multiplying.

Antibiotic resistance: The ability of bacteria to resist the actions of antibiotic drugs.

Soil bacteria: Bacteria found in the soil that destroy other bacteria.

Development of penicillin as an antibiotic. In 1928, British bacteriologist Alexander Fleming (18811955) discovered the bacteria-killing property of penicillin. Fleming noticed that a mold that had accidentally fallen into a bacterial culture in his laboratory had killed the bacteria. Having identified the mold as the fungus Penicillium notatum, Fleming made a juice with it that he named penicillin. After giving it to laboratory mice, he discovered it killed bacteria in the mice without harming healthy body cells. Although Fleming had made an incredible discovery, he was unable to produce penicillin in a form useful to doctors.

It was not until 1941 that two English scientists, Howard Florey (18981968) and Ernst Chain (19061979), developed a form of penicillin that could be used to fight bacterial infections in humans. By 1945, penicillin was available for widespread use and was hailed as the new wonder drug. The antibiotic works by blocking the formation of the bacterial cell wall, thus killing the bacteria. It is still used successfully in the treatment of many bacterial diseases, including strep throat, syphilis (a sexually transmitted disease) and pneumonia. Fleming, Florey, and Chain shared the 1945 Nobel Prize for medicine for their work on penicillin.

The search for other antibiotics

Despite the effectiveness of penicillin, it was soon found that the drug worked against only certain types of bacteria. In 1943, American microbiologist Selman Waksman (18881973) developed the drug streptomycin from soil bacteria. It proved to be particularly effective against

tuberculosis and was used in the treatment of many other bacterial infections. However, streptomycin caused harmful side effects, including hearing loss and vision problems that could lead to blindness.

The discovery of streptomycin led to the development of a new class of drugs called aminoglycosides (pronounced uh-MEE-noh-GLY-kuhzides) that include neomycin (pronounced ne-oh-MY-sin), kanamycin (pronounced kan-uh-MY-sin), and gentamicin (pronounced jen-tuh-MY-sin). These antibiotics work against bacteria that are resistant to penicillin, but they tend to have many of the same side effects as streptomycin and are used only for a short time in cases of serious infection.

Following World War II (193945), drug companies in the United States conducted worldwide searches to find molds and soil bacteria that could be synthesized (made in a lab) into antibiotics. Aureomycin (pronounced aw-ree-oh-MY-sin), the first of the class of antibiotics known as tetracyclines (pronounced teh-truh-SY-kleenz), was discovered in 1945. Another group, the cephalosporins (pronounced seff-uh-low-SPOR-inz), came from a bacteria group living in a drainage pipe on the Italian coast. The antibiotics in this group have effects similar to those of penicillin. Erythromycin (pronounced uh-ree-throw-MY-sin), made from soil bacteria found in the Philippines, is used in patients allergic to penicillin as well as to fight penicillin-resistant bacteria. Bacitracin (pronounced bass-uh-TRAY-sin), an antibiotic made from bacteria, was developed in 1945 and is used as an ointment that is applied directly to the skin.

Resistance to antibiotics

Resistance of bacteria to the effects of antibiotics has become a major problem in the treatment of disease. Bacteria that are not killed or stopped by antibacterial drugs may change in form so that they resist attack against their cell wallsor even produce enzymes that kill the antibiotics. Prescribing antibiotic drugs when they are not needed, not taking the drugs as prescribed, and using the drugs for long periods of time all contribute to the development of resistant strains of bacteria. The use of antibiotics in animal feed to promote animal growth has also led to the development of hardier strains of antibiotic-resistant bacteria. Since the first use of antibiotics in the 1940s, most known bacterial diseases have built up a resistance to one or more antibiotics.

Measures to control the spread of antibiotic-resistant diseases include prescribing the drugs only when necessary, prescribing the correct antibiotic for the disease being treated, and making sure the patient understands the importance of taking all of the prescribed medication. Research in newer types and combinations of drugs is ongoing, as is research in the development of vaccines to prevent bacterial infections.

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Antibiotics

Antibiotics

BRIAN HOYLE

The security and stability of a country depends in part on the health of its citizens. One of the factors that influence the health of people is infectious disease (a disease that can be spread from person to person or from another living being to a human). A variety of infectious diseases are caused by bacteria.

Some bacterial infections can be treated using compounds that are collectively known as antibiotics. Antibiotics can be naturally produced. For example, the first antibiotic discovered (penicillin; discovered in 1928 by Sir Alexander Fleming) is produced by a species of a mold microorganism. There are a variety of different naturally produced antibiotics, while many other antibiotics have been chemically produced. Finally, antibiotics act only on bacteria and are not effective against viruses.

Prior to the discovery of penicillin there were few effective treatments to battle or prevent bacterial infections. Pneumonia, tuberculosis, and typhoid fever were virtually untreatable. And, in those persons whose immune system was not functioning properly, even normally minor bacterial infections could prove to be be life-threatening.

In nature, antibiotics help protect a bacteria or eukaryotic cell (i.e., plant cell) from invading bacteria. In the laboratory, this is evident as the inhibition of growth of bacteria in the presence of the antibiotic-producing species. This screening can be automated so that thousands of samples can be processed each day.

The chemical synthesis of antibiotics is now very sophisticated. The antibiotic can be tailored to affect a specific target on the bacterial cell. Three-dimensional modeling of the bacterial surface and protein molecules is an important aid to antibiotic design.

Penicillin is in a class of antibiotics called beta-lactam antibiotics. The name refers to the chemical ring that is part of the molecule. Other classes of antibiotics include the tetracyclines, aminoglycosides, rifamycins, quinolones, and sulphonamides. The action of these antibiotics is varied. The targets of the antibiotics are different. Some antibiotics disrupt and weaken the cell wall of bacteria (i.e., beta-lactam antibiotics), which causes the bacteria to rupture and die. Other antibiotics disrupt enzymes that are vital for bacterial survival (aminoglycoside antibiotics). Still other antibiotics target genetic material and stop the replication of deoxyribonucleic acid (DNA) (i.e., quinolone antibiotics).

Antibiotics can also vary in the bacteria they affect. Some antibiotics kill only a few related types of bacteria and are referred to as narrow-spectrum antibiotics. Other antibiotics such as penicillin kill a variety of different bacteria. These are the broad-spectrum antibiotics.

Following the discovery of penicillin, many different naturally occurring antibiotics were discovered and still many others were synthesized. They were extremely successful in reducing many infectious diseases. Indeed, in the 1970s the prevailing view was that infectious diseases were a thing of the past. However, beginning in the 1970s and continuing to the present day, resistance to antibiotics is developing.

As of 2002, the problem of antibiotic resistance is so severe that many physicians and security analysts think that the twenty-first century will initiate the "post antibiotic era." In other words, the use of antibiotics to control infectious bacterial disease will no longer be an effective strategy.

Resistance to a specific antibiotic or a class of antibiotics can develop when an antibiotic is overused or misused. If an antibiotic is used properly to treat an infection, then all the infectious bacteria should be killed directly, or weakened such that the host's immune response will kill them. However, if the antibiotic concentration is too low, the bacteria may be weakened but not killed. The same thing can happen if antibiotic therapy is stopped too soon. The surviving bacteria may have acquired resistance, which can be genetically transferred to subsequent generations of bacteria. For example, many strains of Mycobacterium tuberculosis, the bacterium that causes tuberculosis, are resistant to one or more of the antibiotics used to treat the lung infection. Some strains of Staphylococcus aureus that can cause boils, pneumonia, or bloodstream infections, are resistant to most (and with one strain, all) antibiotics.

The increasing antibiotic resistance of bacteria, and the resulting increase in infectious diseases, is a security risk. Disease can decimate the population. The misery and economic hardship that results can cause political instability. In underdeveloped countries, this instability can lead to anger directed at developed countries such as the United States. Even in developed countries, the increasing numbers of people needing hospitalization and medical care can strain the health care system.

The availability of antibiotics to combat bacterial epidemics has always been challenging. The appearance and rapid increase in an infection can tax the ability of a healthcare system to respond with medicines including the appropriate antibiotics.

The threat of biological warfare, such as the aerial distribution of Bacillus anthracis, the agent of anthrax, has made the provision of large quantities of antibiotics a priority for the United States and other nations. Plants that manufacture antibiotics are designed with sterility of manufacture in mind, not security. Disabling an antibiotic manufacturing facility would be a crippling blow to any potential biowarfare response.

Even if a large supply of a particular antibiotic were available, the emergency response would be challenging, as the antibiotic would need to be distributed to many people (i.e., millions in the event of an aerial release of the anthrax bacterium) within hours.

FURTHER READING:

PERIODICALS:

Inglesby, Thomas V. "Bioterrorist Threats: What the Infectious Disease Community Should Know about Anthrax and Plague." Emerging Infections 5. Washington, DC: American Society for Microbiology Press, 2001.

ELECTRONIC:

Central Intelligence Agency. "The Global Infectious Disease Threat and Its Implications for the United States." January 2000.<http://www.cia.gov/cia/publications/nie/report/nie9917d.html> (22 November 2002).

World Health Organization. "Strengthening Global Preparedness for Defense against Infectious Disease Threats." Statement to the United States Senate Committee on Foreign Relations Hearing on The Threat of Bioterrorism and the Spread of Infectious Diseases. 5 September 2001. <http://www.who.int/emc/pdfs/Senate_hearing.pdf>(24 November 2002).

SEE ALSO

Biocontainment Laboratories
Biological Warfare
CDC (United States Centers for Disease Control and Prevention)
L-Gel Decontamination Reagent
Pathogens
Public Health Service (PHS), United States

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Prophylaxis, Antibiotic

Prophylaxis, antibiotic

Definition

A prophylaxis is a measure taken to maintain health and prevent the spread of disease. Antibiotic prophylaxis is the focus of this article and refers to the use of antibiotics to prevent infections.


Purpose

Antibiotics are well known for their ability to treat infections. But some antibiotics also are prescribed to prevent infections. This usually is done only in certain situations or for people with particular medical problems. For example, people with abnormal heart valves have a high risk of developing heart valve infections even after only minor surgery. This happens because bacteria from other parts of the body get into the bloodstream during surgery and travel to the heart valves. To prevent these infections, people with heart valve problems often take antibiotics before having any kind of surgery, including dental surgery.

Antibiotics also may be prescribed to prevent infections in people with weakened immune systems such as those with AIDS or people who are having chemotherapy treatments for cancer. But even healthy people with strong immune systems may occasionally be given preventive antibioticsif they are having certain kinds of surgery that carry a high risk of infection, or if they are traveling to parts of the world where they are likely to get an infection that causes diarrhea, for example.

In all of these situations, a physician should be the one to decide whether antibiotics are necessary. Unless a physician says to do so, it is not a good idea to take antibiotics to prevent ordinary infections.

Because the overuse of antibiotics can lead to resistance, drugs taken to prevent infection should be used only for a short time.

Description

Among the drugs used for antibiotic prophylaxis are amoxicillin (a type of penicillin) and fluoroquinolones such as ciprofloxacin (Cipro) and trovafloxacin (Trovan). These drugs are available only with a physician's prescription and come in tablet, capsule, liquid, and injectable forms.

For surgical prophylaxis, the cephalosporin antibiotics are usually preferred. This class includes cefazolin (Ancef, Kefzol), cefamandole (Mandol), cefotaxime (Claforan), and others. The choice of drug depends on its spectrum and the type of bacteria that are most likely to be encountered. For example, surgery on the intestines, which have many anaerobic bacteria, might call for cefoxitin (Mefoxin), while in heart surgery, where there are no anaerobes, cefazolin might be preferred.


Recommended dosage

The recommended dosage depends on the type of antibiotic prescribed and the reason it is being used. For the correct dosage, the patient is advised to check with the physician or dentist who prescribed the medicine or the pharmacist who filled the prescription. The patient is recommended to be sure to take the medicine exactly as prescribed, and not to take more or less than directed, and to take the medicine only for as long as the physician or dentist says to take it.

The recommended dose of prophylactic antibiotic for surgery has varied with studies. At one time, it was common to give a dose of antibiotic when the patient was called to the operating room , and to continue the drug for 48 hours after surgery. More recent studies indicate that a single antibiotic dose, given immediately before the start of surgery, may be just as effective in preventing infection, while reducing the risk of drug side effects.


Precautions

The warnings listed below refer primarily to the effects of the drugs when taken in multiple doses. When prophylactic antibiotics are used as a single dose, adverse effects are very unlikely. The only exceptions are for people who are allergic to the antibiotic used. Since cephalosporins are closely related to penicillins, people who are allergic to penicillins should avoid cephalosporin antibiotics.

If the medicine causes nausea, vomiting, or diarrhea, the patient is advised to check with the physician or dentist who prescribed it as soon as possible. Patients who are taking antibiotics before surgery should not wait until the day of the surgery to report problems with the medicine. The physician or dentist needs to know right away if problems occur.

For other specific precautions, the patient is advised to see the entry on the type of drug prescribed such as penicillins or fluoroquinolones.


Side effects

Antibiotics may cause a number of side effects. For details, the patient is advised to see entries on specific types of antibiotics. Anyone who has unusual or disturbing symptoms after taking antibiotics should get in contact with the prescribing physician.


Interactions

Whether used to treat or to prevent infection, antibiotics may interact with other medicines. When this happens, the effects of one or both of the drugs may change or the risk of side effects may be greater. Anyone who takes antibiotics for any reason should inform the physician about all the other medicines he or she is taking and should ask whether any possible interactions may interfere with drugs' effects. For details of drug interactions, the candidate is advised to see entries on specific types of antibiotics.


Resources

books

ahfs: drug information. washington dc: american society healthsystems pharmaceuticals, 2002.

reynolds, j.e.f., ed. martindale the extra pharmacopoeia, 31st ed. london: the pharmaceutical press, 1993.

brody, t.m., j. larner, k.p. minneman, and h.c. neu. human pharmacology: molecular to clinical, 2nd ed. st. louis: mosby year-book.

periodicals

braffman-miller, judith. "beware the rise of antibiotic-resistant microbes." usa today (magazine) 125 (march 1997): 56.

"consumer alert: antibiotic resistance is growing!" people's medical society newsletter 16 (august 1997): 1.

guthrie, p. "doctors, patients must act together to save antibiotics' potency, experts say." atlanta journal-constitution (march 19, 2003).


Nancy Ross-Flanigan Sam Uretsky, PharmD

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Ross-Flanigan, Nancy; Uretsky, Sam. "Prophylaxis, Antibiotic." Gale Encyclopedia of Surgery: A Guide for Patients and Caregivers. 2004. Encyclopedia.com. 25 Sep. 2016 <http://www.encyclopedia.com>.

Ross-Flanigan, Nancy; Uretsky, Sam. "Prophylaxis, Antibiotic." Gale Encyclopedia of Surgery: A Guide for Patients and Caregivers. 2004. Encyclopedia.com. (September 25, 2016). http://www.encyclopedia.com/doc/1G2-3406200377.html

Ross-Flanigan, Nancy; Uretsky, Sam. "Prophylaxis, Antibiotic." Gale Encyclopedia of Surgery: A Guide for Patients and Caregivers. 2004. Retrieved September 25, 2016 from Encyclopedia.com: http://www.encyclopedia.com/doc/1G2-3406200377.html

antibiotic

antibiotic, any of a variety of substances, usually obtained from microorganisms, that inhibit the growth of or destroy certain other microorganisms.

Types of Antibiotics

The great number of diverse antibiotics currently available can be classified in different ways, e.g., by their chemical structure, their microbial origin, or their mode of action. They are also frequently designated by their effective range. Tetracyclines, the most widely used broad-spectrum antibiotics, are effective against both Gram-positive and Gram-negative bacteria, as well as against rickettsias and psittacosis-causing organisms (see Gram's stain). Ciprofloxacin (Cipro) is another broad-spectrum antibiotic, effective in the treatment of mild infections of the urinary tract and sinuses. The medium-spectrum antibiotics bacitracin, the erythromycins, penicillin, and the cephalosporins are effective primarily against Gram-positive bacteria, although the streptomycin group is effective against some Gram-negative and Gram-positive bacteria. Polymixins are narrow-spectrum antibiotics effective against only a few species of bacteria.

Administration and Side Effects

Antibiotics are either injected, given orally, or applied to the skin in ointment form. Many, while potent anti-infective agents, also cause toxic side effects. Some, like penicillin, are highly allergenic and can cause skin rashes, shock, and other manifestations of allergic sensitivity. Others, such as the tetracyclines, cause major changes in the intestinal bacterial population and can result in superinfection by fungi and other microorganisms. Chloramphenicol, which is now restricted in use, produces severe blood diseases, and use of streptomycin can result in ear and kidney damage. Many antibiotics are less effective than formerly because antibiotic-resistant strains of microorganisms have emerged (see drug resistance).

Nonmedical Use

Antibiotics have found wide nonmedical use. Some are used in animal husbandry, along with vitamin B12, to enhance the weight gain of livestock. Some authorities believe the addition of antibiotics to animal feeds is dangerous because continuous low exposure to the antibiotic can sensitize humans to the drug and make them unable to take the substance later for the treatment of infection. In addition, low levels of antibiotics in animal feed encourage the emergence of antibiotic-resistant strains of microorganisms. Drug resistance has been shown to be carried by a genetic particle transmissible from one strain of microorganism to another, and the presence of low levels of antibiotics can actually cause an increase in the number of such particles in the bacterial population and increase the probability that such particles will be transferred to pathogenic, or disease-causing, strains. In 2013 the Food and Drug Administration moved to restrict the use of antibiotics in livestock, calling for labeling changes that would bar their use to promote growth and requirements for veterinarian supervision when antibiotics are used. The use of antibiotics for disease prevention (as opposed to disease treatment) was not, however, banned. Antibiotics have also been used to treat plant diseases such as bacteria-caused infections in tomatoes, potatoes, and fruit trees. The substances are also used in experimental research.

Production of Antibiotics

The mass production of antibiotics began during World War II with streptomycin and penicillin. Now most antibiotics are produced by staged fermentations in which strains of microorganisms producing high yields are grown under optimum conditions in nutrient media in fermentation tanks holding several thousand gallons. The mold is strained out of the fermentation broth, and then the antibiotic is removed from the broth by filtration, precipitation, and other separation methods. In some cases new antibiotics are laboratory synthesized, while many antibiotics are produced by chemically modifying natural substances; many such derivatives are more effective than the natural substances against infecting organisms or are better absorbed by the body, e.g., some semisynthetic penicillins are effective against bacteria resistant to the parent substance.

History

Although for centuries preparations derived from living matter were applied to wounds to destroy infection, the fact that a microorganism is capable of destroying one of another species was not established until the latter half of the 19th cent. when Pasteur noted the antagonistic effect of other bacteria on the anthrax organism and pointed out that this action might be put to therapeutic use. Meanwhile the German chemist Paul Ehrlich developed the idea of selective toxicity: that certain chemicals that would be toxic to some organisms, e.g., infectious bacteria, would be harmless to other organisms, e.g., humans.

In 1928, Sir Alexander Fleming, a Scottish biologist, observed that a common mold (genus Penicillium) had destroyed staphylococcus bacteria in culture, and in 1939 the American microbiologist René Dubos demonstrated that a soil bacterium was capable of decomposing the starchlike capsule of the pneumococcus bacterium, without which the pneumococcus is harmless and does not cause pneumonia. Dubos then found in the soil a microbe, Bacillus brevis, from which he obtained a product, tyrothricin, that was highly toxic to a wide range of bacteria. Tyrothricin, a mixture of the two peptides gramicidin and tyrocidine, was also found to be toxic to red blood and reproductive cells in humans but could be used to good effect when applied as an ointment on body surfaces. Penicillin was finally isolated in 1939, and in 1944 Selman Waksman and Albert Schatz, American microbiologists, isolated streptomycin and a number of other antibiotics from Streptomyces griseus.

See also actinomycin, amphotericin B, ampicillin, lincomycin, neomycin, rifampin, and vancomycin.

Bibliography

See H. M. Böttcher, Wonder Drugs (1964); T. Korzybski, Antibiotics (2 vol., 1967); L. P. Garrod et al., Antibiotics and Chemotherapy (3d ed. 1971); M. J. Blaser, Missing Microbes (2014).

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antibiotics

antibiotics have come to be regarded in the minds of most people as substances used to combat infection. In fact they are both more and less than that; more because they are increasingly important in the chemotherapy of cancer, and less because not all drugs used to treat microbial infections are actually antibiotics. Antibiotics are substances of natural origin, and their name derives from the ecological relationship between the organism which produces them and the microbe or living tissue whose growth is inhibited by them: antibiosis — the exact antithesis of symbiosis (living together for mutual benefit). Antibiosis as a biological phenomenon was known in the nineteenth century, but the scientific term ‘antibiotic’ was only coined much later, after the young physician Alexander Fleming (later Sir Alexander) had made his seminal observations which led to the discovery of penicillin and ushered in the era of modern chemotherapy. As the story goes, in 1929 Fleming was working at St Mary's Hospital in Paddington with cultures of pathogenic bacteria (staphylococci), when one day there blew in through the partially open window of his laboratory above Praed Street a fungal spore, which landed on one of his agar plates and grew up to produce a large clump of the mould. For an ordinary microbiologist this could have been regarded as a minor inconvenience, the sort of contamination which happens from time to time if one is not super-meticulous about sterile precautions, and calls for nothing more demanding than the disposal of the contaminated plate and inoculation of a fresh one. To his credit, Fleming noticed that not only was the growth of the bacteria inhibited in the vicinity of the mould, but the colonies of staphylococci were actually disappearing or lysing. He showed that the effect was due to a substance secreted by the mould, and attempted to purify it — but it proved unstable.

It took the outbreak of World War II to galvanize the scientific community into action and exploit the discovery of penicillin for widespread clinical benefit. The problems of producing the material on an industrial scale were solved, and for the first time many infectious diseases were brought under effective control. But not all. In general, infections caused by ‘Gram positive’ bacteria (categorized by Gram's staining process) proved curable by penicillin, but treatment of those caused by ‘Gram negative’ organisms (such as dysentery, cholera, and the like) had to await the discovery of other antibiotics by screening methods which are still largely in use today. Streptomycin, tetracyclines, and numerous macrolide (‘large-ring’) antibiotics were found whose activities complemented those of penicillin. In parallel with screening approaches the chemists succeeded in creating a whole family of semi-synthetic derivatives of penicillin (generically known as β-lactam antibiotics, because they all contain the essential 4-membered β-lactam ring). These semi-synthetic drugs have extended the antibacterial spectrum of ‘natural’ penicillin, and have helped to counter the emergence of antibiotic-resistant strains of pathogenic bacteria.

Antibiotics work by selectively inhibiting processes which are peculiar to microbial cells, often ones associated with a unique structural feature, enzyme, or organelle not present in human cells. A prime example is the bacterial cell wall, the composition of which is unique in several respects. Penicillins are selectively toxic because they mimic a particular dipeptide sequence present in cell wall precursors. This molecular mimicry inactivates a crucial enzyme needed to form cross-links between the peptidoglycan chains which impart mechanical strength to the bacterial cell wall. Other antibiotics prevent protein synthesis in the bacterial cell, or inactivate enzymes concerned with the complicated processes of nucleotide and nucleic acid biosynthesis.

M. J. Waring


See also chemotherapy; infection.

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COLIN BLAKEMORE and SHELIA JENNETT. "antibiotics." The Oxford Companion to the Body. 2001. Encyclopedia.com. 25 Sep. 2016 <http://www.encyclopedia.com>.

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Antibiotics

ANTIBIOTICS

Antibiotics represent a class of drugs used in the treatment of infections and infectious diseases caused by bacteria. These bacteria possess unique features (e.g., a cell wall, proteins, enzymes) that differentiate them from animal cells. Antibiotics interfere with the production of these bacterial characteristics, resulting in selective killing or growth inhibition of susceptible microorganisms. For example, prior to 1990, infections caused by Streptococcus pneumoniae (e.g., pneumonia, bronchitis, ear infections), were usually treated with penicillin or amoxicillin. Streptococcus pneumoniae possess a cell wall that acts as a protective barrier a unique feature not found on animal or human cells. Penicillin or amoxicillin, two common antibiotics, bind to that cell wall as it is produced, causing it to weaken and "leak," eventually killing the bacteria without harming the animal host cells.

Antibiotics can be further described by the number of bacteria covered (narrow-spectrum antibiotics versus broad-spectrum antibiotics), and by how strongly the antibiotics work against the bacteria (bactericidal activity versus bacteriostatic activity). Narrow-spectrum antibiotics are used to treat infections limited to a few families and types of bacteria, while broad-spectrum antibiotics are useful to treat infections caused by multiple families of bacteria. An antibiotic that exhibits bactericidal activity will kill bacteria when it comes into contact with it (e.g., S. pneumoniae ). Bacteriostatic activity, on the other hand, occurs when an antibiotic inhibits the growth of bacteria, without necessarily killing it.

Meganne S. Kanatani

(see also: Communicable Disease Control; Drug Resistance; Pathogenic Organisms; Penicillin; Pharmaceutical Industry )

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antibiotic

antibiotic Substance that is capable of stopping the growth of, or destroying, bacteria and other microorganisms. Antibiotics are germicides that are safe enough to be eaten or injected into the body. The post-1945 introduction of antibiotics has revolutionized medical science, making possible the virtual elimination of once widespread and often fatal diseases, including typhoid fever, plague and cholera. Some antibiotics are selective – that is, effective against specific microorganisms; those effective against a large number of microorganisms are known as broad-spectrum antibiotics. Important antibiotics include penicillin, the first widely used antibiotic, streptomycin and the tetracyclines. Some bacteria have developed antibiotic resistance. See also antiseptic

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antibiotic

antibiotic An antimetabolite obtained from or produced by a living bacterium, fungus, or plant, which, in very small amounts, is toxic or lethal to other organisms (usually other bacteria or fungi). The term may also refer to chemical derivatives of naturally occurring antibiotics or to synthetic substances with similar properties. Under natural conditions the ability to produce an antibiotic presumably confers a competitive advantage on the organism. Some antibiotics are important in the treatment of animal diseases caused by micro-organisms (e.g., in humans chloramphenicol (developed in 1947) is active against many bacterial infections, including those that cause typhoid and rickettsial fevers).

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antibiotics

antibiotics Substances produced by living organisms which inhibit the growth of other organisms. The first antibiotic to be discovered was penicillin, which is produced by the mould Penicillium notatum and inhibits the growth of sensitive bacteria. Many antibiotics are used to treat bacterial infections in human beings and animals; different compounds affect different bacteria. Small amounts of antibiotics may be added to animal feed (a few grams/tonne), resulting in improved growth, possibly by controlling mild infections or changing the population of intestinal bacteria and so altering the digestion and absorption of food, but their use as growth promoters is banned in the EU.

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antibiotic

antibiotic An antimetabolite obtained from or produced by a living bacterium, fungus, or plant, which, in very small amounts, is toxic or lethal to other organisms (usually other bacteria or fungi). The term may also refer to chemical derivatives of naturally occurring antibiotics or to synthetic substances with similar properties. Under natural conditions the ability to produce an antibiotic presumably confers a competitive advantage on the organism. Some antibiotics are important in the treatment of animal diseases caused by micro-organisms.

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antibiotics

antibiotics Substances that destroy or inhibit the growth of microorganisms, particularly disease-producing bacteria and fungi. Antibiotics are obtained from microorganisms (especially moulds) or synthesized. Common antibiotics include the penicillins, streptomycin, and tetracyclines. They are used to treat various infections but tend to weaken the body's natural defence mechanisms and can cause allergies. Overuse of antibiotics can lead to the development of resistant strains of microorganisms.

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antibiotic

antibiotic (anti-by-ot-ik) n. a substance, produced by or derived from a microorganism, that destroys or inhibits the growth of other microorganisms. Antibiotics are used to treat infections caused by organisms that are sensitive to them, usually bacteria or fungi. See also aminoglycosides, antifungal, antiviral drug, cephalosporin, penicillin, quinolone, tetracyclines.

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antibiotic

an·ti·bi·ot·ic / ˌantēbīˈätik; ˌantī-/ • n. a medicine (such as penicillin or its derivatives) that inhibits the growth of or destroys microorganisms. • adj. relating to, involving, or denoting antibiotics.

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antibiotic

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