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Anticoagulant and Antiplatelet Drugs

Anticoagulant and antiplatelet drugs

Definition

Anticoagulants are drugs used to prevent clot formation or to prevent a clot that has formed from enlarging. They inhibit clot formation by blocking the action of clotting factors or platelets. Anticoagulant drugs fall into one of three categories: inhibitors of clotting factor synthesis, inhibitors of thrombin, and antiplatelet drugs.


Purpose

Anticoagulant drugs reduce the ability of the blood to form clots. Although blood clotting is essential to prevent serious bleeding in the case of skin cuts, clots inside the blood vessels block the flow of blood to major organs and cause heart attacks and strokes. Although these drugs are sometimes called blood thinners, they do not actually thin the blood. Furthermore, this type of medication will not dissolve clots that already have formed, although the drug stops an existing clot from worsening. However, another type of drug, used in thrombolytic therapy , will dissolve existing clots.

Anticoagulant drugs are used for a number of conditions. For example, they may be given to prevent blood clots from forming after the replacement of a heart valve or to reduce the risk of a stroke or another heart attack after a first heart attack. They are also used to reduce the chance of blood clots forming during open-heart surgery or bypass surgery. Low doses of these drugs may be given to prevent blood clots in patients who must stay in bed for a long time after certain types of surgery. They may also be used to prevent the formation of clots in needles or tubes that are inserted into veins, such as indwelling catheters.

Anticoagulants may be given after major surgery to prevent the formation of clots due to lack of physical activity. Patients who are unable to move around may be at risk of developing clots, particularly in the legs. Anticoagulants are given to prevent this. At the same time, compression stockings may be used to reduce the risk of clots in the legs. Compression stocks are worn on the lower legs, and act by increasing the pressure on the veins of the leg, then relaxing. The compression-relaxation keeps the blood in the veins moving, and reduces the risk of clots following surgery.

Because anticoagulants affect the blood's ability to clot, they can increase the risk of severe bleeding and heavy blood loss. It is thus essential to take these drugs exactly as directed and to see a physician regularly as long as they are prescribed. With some of these drugs, regular blood tests, as often as once a day, may be required.


Description

Most anticoagulant drugs are available only with a physician's prescription. They come in tablet and injectable forms. They fall into three groups:

  • Inhibitors of clotting factor synthesis. These anticoagulants inhibit the production of certain clotting factors in the liver. One example is warfarin (brand name: Coumadin).
  • Inhibitors of thrombin. These drugs interfere with blood clotting by blocking the activity of thrombin. They include heparin and lepirudin (Refludan).
  • Antiplatelet drugs. These drugs interact with platelets, which is a type of blood cell, to block platelets from aggregating into harmful clots. They include aspirin , ticlopidine (Ticlid), clopidogrel (Plavix), tirofiban (Aggrastat), and eptifibatide (Integrilin).

Recommended dosage

The recommended dosage depends on the type of anticoagulant drug and the medical condition for which it is prescribed. The prescribing physician or the pharmacist who fills the prescription can provide information concerning the correct dosage. Usually, the physician will adjust the dose after checking the patient's clotting time.

Anticoagulant drugs must be taken exactly as directed by the physician. Larger or more frequent doses should not be taken, and the drug should also not be taken for longer than prescribed. Taking too much of this medication can cause easy bruising or severe bleeding. Anticoagulants should also be taken on schedule. A record of each dose should be kept as it is taken. If a dose is missed, it should be taken as soon as possible followed by the regular dose schedule. However, a patient who forgets to take a missed dose until the next day should not take the missed dose at all and should not double the next dose, as this could lead to bleeding. A record of all missed doses should be kept for the prescribing physician who should be informed at the scheduled visits.


Precautions

Persons who take anticoagulants should see a physician regularly while taking these drugs, particularly at the beginning of therapy. The physician will order periodic blood tests to check the blood's clotting ability. The results of these tests will help the physician determine the proper amount of medication to be taken each day.

Time is required for normal clotting ability to return after anticoagulant treatment. During this period, patients must observe the same precautions they observed while taking the drug. The length of time needed for the blood to return to normal depends on the type of anticoagulant drug that was taken. The prescribing physician will advise as to how long the precautions should be observed.

People who are taking anticoagulant drugs should tell all physicians, dentists, pharmacists, and other medical professionals who provide them with medical treatments or services that they are taking such a medication. They should also carry identification stating that they are using an anticoagulant drug.

Other prescription drugs or over-the-counter medicineespecially aspirinshould be not be taken without the prescribing physician being informed.

Because of the risk of heavy bleeding, anyone who takes an anticoagulant drug must take care to avoid injuries. Sports and other potentially hazardous activities should be avoided. Any falls, blows to the body or head, or other injuries should be reported to a physician, as internal bleeding may occur without any obvious symptoms. Special care should be taken in shaving and in brushing and flossing the teeth. Soft toothbrushes should be used and the flossing should be very gentle. Electric razors should be used instead of a blade.

Alcohol can change the way anticoagulant drugs affect the body. Anyone who takes this medicine should not have more than one to two alcoholic drinks at any one time, and should not drink alcohol every day.


Special conditions

People with specific medical conditions or who are taking certain other medicines can have problems if they take anticoagulant drugs. Before taking these drugs, the prescribing physician should be informed about any of these conditions.

allergies. Anyone who has had unusual reactions to anticoagulants in the past should let the physician know before taking the drugs again. The physician should also be told about any allergies to beef, pork, or other foods; dyes; preservatives; or other substances.

pregnancy. Anticoagulants may cause many serious problems if taken during pregnancy. Birth defects, severe bleeding in the fetus, and other problems that affect the physical or mental development of the fetus or newborn are possible. The mother may also experience severe bleeding if she takes anticoagulants during pregnancy, during delivery, or even shortly after delivery. Women should not start taking anticoagulants during pregnancy and should not become pregnant while taking the drug. Any woman who becomes pregnant or suspects that she has become pregnant while taking an anticoagulant should check with her physician immediately.

breastfeeding. Some anticoagulant drugs may pass into breast milk. Blood tests can be done on nursing babies to see whether the drug is causing any problems. If it is, other medication may be prescribed to counteract the effects of the anticoagulant drug.

other medical conditions. Before using anticoagulant drugs, people should inform their physician about any medical problems they have. They should also let the physician who prescribed the medicine know if they are being treated by any other medical physician or dentist. In addition, people who will be taking anticoagulant drugs should let their physician know if they have recently had any of the following:

  • fever lasting more than one to two days
  • severe or continuing diarrhea
  • childbirth
  • heavy or unusual menstrual bleeding
  • insertion of an intrauterine contraceptive device (i.e., IUD)
  • falls, injuries, or blows to the body or head
  • any type of surgery, including dental surgery
  • spinal anesthesia
  • radiation treatment
  • any intestinal condition

Side effects

The most common minor side effects are bloating or gas. These problems usually go away as the body adjusts to the drug and do not require medical treatment.

More serious side effects may occur, especially if excessive anticoagulant is taken. If any of the following side effects occur, a physician should be notified immediately:

  • bleeding gums
  • sores or white spots in the mouth or throat
  • unusual bruises or purplish areas on the skin
  • unexplained nosebleeds
  • unusually heavy bleeding or oozing from wounds
  • unexpected or unusually heavy menstrual bleeding
  • blood in the urine
  • cloudy or dark urine
  • painful or difficult urination or sudden decrease in amount of urine
  • black, tarry, or bloody stools
  • coughing up blood
  • vomiting blood or something that looks like coffee grounds
  • constipation
  • pain or swelling in the stomach or abdomen
  • back pain
  • stiff, swollen, or painful joints
  • painful, bluish or purplish fingers or toes
  • puffy or swollen eyelids, face, feet, or lower legs
  • changes in the color of the face
  • skin rash, itching, or hives
  • yellow eyes or skin
  • severe or continuing headache
  • sore throat and fever, with or without chills
  • breathing problems or wheezing
  • tightness in the chest
  • dizziness
  • unusual tiredness or weakness
  • weight gain

In addition, patients taking anticoagulant drugs should check with their physicians as soon as possible if any of these side effects occur:

  • nausea or vomiting
  • diarrhea
  • stomach pain or cramps

Other side effects may occur. Anyone who has unusual symptoms while taking anticoagulant drugs should get in touch with the prescribing physician.

Interactions

Anticoagulants may interact with many other medications. When this happens, the effects of one or both of the drugs may change or the risk of side effects may be increased. Anyone who takes anticoagulants should inform the prescribing physician about other prescription or nonprescription (over-the-counter) medicines he or she is takingeven aspirin, laxatives , vitamins, and antacids.

Diet also affects the way anticoagulant drugs work in the body. A normal, balanced diet should be followed every day while taking such medication. No dietary changes should be made without informing first the prescribing physician, who should also be told of any illness or other condition interfering with the ability to eat normally. Diet is a very important consideration because the amount of vitamin K in the body affects how anticoagulant drugs work. Dicoumarol and warfarin act by reducing the effects of vitamin K, which is found in meats, dairy products, leafy, green vegetables, and some multiple vitamins and nutritional supplements. For the drugs to work properly, it is best to have the same amount of vitamin K in the body all the time. Foods containing vitamin K should not be increased or decreased without consulting with the prescribing physician. If the patient takes vitamin supplements, he or she should check the label to see if it contains vitamin K. Because vitamin K is also produced by intestinal bacteria, a severe case of diarrhea or the use of laxatives may also alter a person's vitamin K levels.


Resources

books

AHFS: Drug Information. Washington, DC: American Society Healthsystems Pharmaceuticals, 2002.

Brody, T.M., J. Larner, K.P. Minneman, H.C. Neu. Human Pharmacology: Molecular to Clinical, 2nd ed. St. Louis: Mosby Year-Book.

Reynolds, J.E.F., ed. Martindale: The Extra Pharmacopoeia, 31st ed. London: The Pharmaceutical Press, 1993.

other

"Abciximab." Medline Plus Drug Information. [cited May 2003]/<http://www.nlm.nih.gov/medlineplus/druginfo/uspdi/500417.html>.

"Heparin (Systemic)." Medline Plus Drug Information. [cited May 2003]. <http://www.nlm.nih.gov/medlineplus/druginfo/uspdi/202280.html>.

"Salicylates (Systemic)." Medline Plus Drug Information. [cited May 2003]. <http://www.nlm.nih.gov/medlineplus/druginfo/uspdi/202515.html>.

"Warfarin." Medline Plus Drug Information. [cited May 2003]. <http://www.nlm.nih.gov/medlineplus/druginfo/med master/a682277.html>.

Nancy Ross-Flanigan Sam Uretsky

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Ross-Flanigan, Nancy; Uretsky, Sam. "Anticoagulant and Antiplatelet Drugs." Gale Encyclopedia of Surgery: A Guide for Patients and Caregivers. 2004. Encyclopedia.com. 28 May. 2016 <http://www.encyclopedia.com>.

Ross-Flanigan, Nancy; Uretsky, Sam. "Anticoagulant and Antiplatelet Drugs." Gale Encyclopedia of Surgery: A Guide for Patients and Caregivers. 2004. Encyclopedia.com. (May 28, 2016). http://www.encyclopedia.com/doc/1G2-3406200037.html

Ross-Flanigan, Nancy; Uretsky, Sam. "Anticoagulant and Antiplatelet Drugs." Gale Encyclopedia of Surgery: A Guide for Patients and Caregivers. 2004. Retrieved May 28, 2016 from Encyclopedia.com: http://www.encyclopedia.com/doc/1G2-3406200037.html

Anticoagulant and Antiplatelet Drugs

Anticoagulant and Antiplatelet Drugs

Definition

Anticoagulants are drugs used to prevent clot formation or to prevent a clot that has formed from enlarging. They inhibit clot formation by blocking the action of clotting factors or platelets. Anticoagulant drugs fall into three categories: inhibitors of clotting factor synthesis, inhibitors of thrombin and antiplatelet drugs.

Purpose

Anticoagulant drugs reduce the ability of the blood to form clots. Although blood clotting is essential to prevent serious bleeding in the case of skin cuts, clots inside the blood vessels block the flow of blood to major organs and cause heart attacks and strokes. Although these drugs are sometimes called blood thinners, they do not actually thin the blood. Furthermore, this type of medication will not dissolve clots that already have formed, although the drug stops an existing clot from worsening. However, another type of drug, used in thrombolytic therapy, will dissolve existing clots.

Anticoagulant drugs are used for a number of conditions. For example, they may be given to prevent blood clots from forming after the replacement of a heart valve or to reduce the risk of a stroke or another heart attack after a first heart attack. They are also used to reduce the chance of blood clots forming during open heart surgery or bypass surgery. Low doses of these drugs may be given to prevent blood clots in patients who must stay in bed for a long time after certain types of surgery.

Because anticoagulants affect the blood's ability to clot, they can increase the risk of severe bleeding and heavy blood loss. It is thus essential to take these drugs exactly as directed and to see a physician regularly as long as they are prescribed.

Description

Anticoagulant drugs, also called anticlotting drugs or blood thinners, are available only with a physician's prescription. They come in tablet and injectable forms. They fall into three groups:

  • Inhibitors of clotting factor synthesis. These anticoagulants inhibit the production of certain clotting factors in the liver. One example is warfarin (brand name: coumadin).
  • Inhibitors of thrombin. Thrombin inhibitors interfere with blood clotting by blocking the activity of thrombin. They include heparin, lepirudin (Refludan).
  • Antiplatelet drugs. Antiplatelet drugs interact with platelets, which is a type of blood cell, to block platelets from aggregating into harmful clots. They include: aspirin, ticlopidine (Ticlid), clopidogrel (Plavix), tirofiban (Aggrastat), and eptifibatide (Integrilin).

Recommended dosage

The recommended dosage depends on the type of anticoagulant drug and the medical condition for which it is prescribed. The prescribing physician or the pharmacist who filled the prescription can provide information concerning the correct dosage. Usually, the physician will adjust the dose after checking the patient's clotting time.

KEY TERMS

Anticoagulant Drug used to prevent clot formation or to prevent a clot that has formed from enlarging. Anticoagulant drugs inhibit clot formation by blocking the action of clotting factors or platelets. Anticoagulant drugs fall into three groups: inhibitors of clotting factor synthesis, inhibitors of thrombin and antiplatelet drugs.

Antiplatelet drug Drug that inhibits platelets from aggregating to form a plug. They are used to prevent clotting and alter the natural course of atherosclerosis.

Atherosclerosis Condition characterized by deposits of fatty plaque in the arteries.

Clot A soft, semi-solid mass that forms when blood gels.

Platelet A small, disk-shaped body in the blood that has an important role in blood clotting: they form the initial plug at the rupture site of a blood vessel.

Thrombin Thrombin is a protein produced by the body. It is a specific clotting factor that plays an important role in the blood clotting process.

Thrombin inhibitor Thrombin inhibitors are one type of anticoagulant medication, used to help prevent formation of harmful blood clots in the body by blocking the activity of thrombin.

Anticoagulant drugs must be taken exactly as directed by the physician. Larger or more frequent doses should not be taken, and the drug should also not be taken for longer than prescribed. Taking too much of this medication can cause severe bleeding. Anticoagulants should also be taken on schedule. A record of each dose should be kept as it is taken. If a dose is missed, it should be taken as soon as possible followed by the regular dose schedule. However, a patient who forgets to take a missed dose until the next day should not take the missed dose at all and should not double the next dose, as this could lead to bleeding. A record of all missed doses should be kept for the prescribing physician who should be informed at the scheduled visits.

Precautions

Persons who take anticoagulants should see a physician regularly while taking these drugs, particularly at the beginning of therapy. The physician will order periodic blood tests to check the blood's clotting ability. The results of these tests will help the physician determine the proper amount of medication to be taken each day.

Time is required for normal clotting ability to return after anticoagulant treatment. During this period, patients must observe the same precautions they observed while taking the drug. The length of time needed for the blood to return to normal depends on the type of anticoagulant drug that was taken. The prescribing physician will advise as to how long the precautions should be observed.

People who are taking anticoagulant drugs should tell all physicians, dentists, pharmacists, and other medical professionals who provide medical treatments or services to them that they are taking such a medication. They should also carry identification stating that they are using an anticoagulant drug.

Other prescription drugs or over-the-counter medicine-especially aspirin-should be not be taken without the prescribing physician being informed.

Because of the risk of heavy bleeding, anyone who takes an anticoagulant drug must take care to avoid injuries. Sports and other potentially hazardous activities should be avoided. Any falls, blows to the body or head, or other injuries should be reported to a physician, as internal bleeding may occur without any obvious symptoms. Special care should be taken in shaving and in brushing and flossing the teeth. Soft toothbrushes should be used and the flossing should be very gentle. Electric razors should be used instead of a blade.

Alcohol can change the way anticoagulant drugs affect the body. Anyone who takes this medicine should not have more than one to two drinks at any time and should not drink alcohol every day.

Special conditions

People with specific medical conditions or who are taking certain other medicines can have problems if they take anticoagulant drugs. Before taking these drugs, the prescribing physician should be informed about any of these conditions:

ALLERGIES. Anyone who has had unusual reactions to anticoagulants in the past should let his or her physician know before taking the drugs again. The physician should also be told about any allergies to beef, pork, or other foods; dyes; preservatives; or other substances.

PREGNANCY. Anticoagulants may cause many serious problems if taken during pregnancy. Birth defects, severe bleeding in the fetus, and other problems that affect the physical or mental development of the fetus or newborn are possible. The mother may also experience severe bleeding if she takes anticoagulants during pregnancy, during delivery, or even shortly after delivery. Women should not take start taking anticoagulants during pregnancy and should not become pregnant while taking it. Any woman who becomes pregnant or suspects that she has become pregnant while taking an anticoagulant should check with her physician immediately.

BREASTFEEDING. Some anticoagulant drugs may pass into breast milk. Blood tests can be done on nursing babies to see whether the drug is causing any problems. If it is, other medication may be prescribed to counteract the effects of the anticoagulant drug.

OTHER MEDICAL CONDITIONS. Before using anticoagulant drugs, people should inform their physician about any medical problems they have. They should also let the physician who prescribed the medicine know if they are being treated by any other medical physician or dentist. In addition, people who will be taking anticoagulant drugs should let their physician know if they have recently had any of the following:

  • fever lasting more than one to two days
  • severe or continuing diarrhea
  • childbirth
  • heavy or unusual menstrual bleeding
  • insertion of an intrauterine contraceptive device (IUD)
  • falls, injuries, or blows to the body or head
  • any type of surgery, including dental surgery
  • spinal anesthesia
  • radiation treatment

USE OF CERTAIN FOODS AND MEDICINES. Many foods and drugs may affect the way the anticoagulant drugs work or may increase the risk of side effects.

Side effects

The most common minor side effects are bloating or gas. These problems usually go away as the body adjusts to the drug and do not require medical treatment.

More serious side effects may occur, especially if excessive anticoagulant is taken. If any of the following side effects occur, a physician should be notified immediately:

  • bleeding gums
  • sores or white spots in the mouth or throat
  • unusual bruises or purplish areas on the skin
  • unexplained nosebleeds
  • unusually heavy bleeding or oozing from wounds
  • unexpected or unusually menstrual bleeding
  • blood in the urine
  • cloudy or dark urine
  • painful or difficult urination or sudden decrease in amount of urine
  • black, tarry, or bloody stools
  • coughing up blood
  • vomiting blood or something that looks like coffee grounds
  • constipation
  • pain or swelling in the stomach or abdomen
  • back pain
  • stiff, swollen, or painful joints
  • painful, bluish or purplish fingers or toes
  • puffy or swollen eyelids, face, feet, or lower legs
  • changes in the color of the face
  • skin rash, itching, or hives
  • yellow eyes or skin
  • severe or continuing headache
  • sore throat and fever, with or without chills
  • breathing problems or wheezing
  • tightness in the chest
  • dizziness
  • unusual tiredness or weakness
  • weight gain.

In addition, patients taking anticoagulant drugs should check with their physicians as soon as possible if any of these side effects occur:

  • nausea or vomiting
  • diarrhea
  • stomach pain or cramps.

Other side effects may occur. Anyone who has unusual symptoms while taking anticoagulant drugs should get in touch with his or her physician.

Interactions

Anticoagulants may interact with many other medications. When this happens, the effects of one or both of the drugs may change or the risk of side effects may be increased. Anyone who takes anticoagulants should inform the prescribing physician about other prescription or nonprescription (over-the-counter medicines) he or she is taking-even aspirin, laxatives, vitamins, and antacids.

Diet also affects the way anticoagulant drugs work in the body. A normal, balanced diet should be followed every day while taking such medication. No dietary changes should be made without informing first the prescribing physician, who should also be told of any illness or other condition interfering with the ability to eat normally. Diet is a very important consideration because the amount of vitamin K in the body affects how anticoagulant drugs work. Dicoumarol and warfarin act by reducing the effects of vitamin K. Vitamin K is found in meats, dairy products, leafy, green vegetables, and some multiple vitamins and nutritional supplements. For the drugs to work properly, it is best to have the same amount of vitamin K in the body all the time. Foods containing vitamin K in the diet should not be increased or decreased without consulting with the prescribing physician. If the patient takes vitamin supplements, he should check the label to see if it contains vitamin K. Because vitamin K is also produced by intestinal bacteria, a severe case of diarrhea or the use of laxatives may also alter a person's vitamin K levels.

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Ross-Flanigan, Nancy. "Anticoagulant and Antiplatelet Drugs." Gale Encyclopedia of Medicine, 3rd ed.. 2006. Encyclopedia.com. 28 May. 2016 <http://www.encyclopedia.com>.

Ross-Flanigan, Nancy. "Anticoagulant and Antiplatelet Drugs." Gale Encyclopedia of Medicine, 3rd ed.. 2006. Encyclopedia.com. (May 28, 2016). http://www.encyclopedia.com/doc/1G2-3451600123.html

Ross-Flanigan, Nancy. "Anticoagulant and Antiplatelet Drugs." Gale Encyclopedia of Medicine, 3rd ed.. 2006. Retrieved May 28, 2016 from Encyclopedia.com: http://www.encyclopedia.com/doc/1G2-3451600123.html

Anticoagulant

Anticoagulant

Anticoagulants are substances that inhibit coagulation (clotting) of the blood. They are used to keep stored blood for transfusions from clotting, to treat conditions involving dangerous blood clotting (includings strokes and heart disease), and in situations where there is a serious risk of dangerous clotting, such as during certain surgical procedures.

For centuries, medical practitioners had used leeches to suck blood from patients. In 1884 J. B. Haycraft showed that blood flowed freely during this procedure because the leeches secreted an anticoagulant (anti-clotting) factor. A dry, powdered extract of leeches' heads called hirudin was introduced around 1900 and used in physiological experiments (tests relating to the functioning of the human body), although it was not used in clinical practice. New research on hirudin in the 1990s has led to an experimental drug shown to be safe and effective. Although production of this substance is currently expensive, it may eventually provide another anticoagulant option.

Prior to the discovery of hirudin, donated blood tended to clot before it was absorbed into the recipient's blood system; as a result, transfusions were not always effective. In 1869, sodium phosphate was introduced as an anticoagulant to overcome this problem. In 1914 sodium citrate was also shown to be an effective anticoagulant for donated blood. Sodium citrate's use was of great value during World War I (1914-1918) and became the standard by 1917.

Heparin

The main anticoagulants used today, are heparin, which is injected, and coumarin, which is taken orally (by mouth). Heparin was discovered in 1916 by Jay McLean (1890-1957), a medical student. McLean was studying at Johns Hopkins University under William Ho well (1860-1945), who had been investigating blood coagulation for years. McLean took on the project of preparing pure samples of cephalin, a clotting substance obtained from brain tissue. While extracting compounds similar to cephalin from heart and liver tissue, McLean discovered that the liver extract did not cause blood to clot. McLean called the extract heparphosphatid.

After McLean left Johns Hopkins, Howell continued working on the liver extract, aided by Emmett Holt (1855-1924). The researchers developed ways to extract an improved water-soluble anticoagulant from liver, which they named heparin in 1918. Howell continued his work on heparin during the 1920s, while Charles Best (1899-1978), David Scott, and Arthur Charles of the University of Toronto worked with heparin extracted from beef liver. They eventually developed practical methods for purifying and standardizing the drug. Clinical trials followed. The success of the artificial kidney in 1944 and the later development of heartlung bypass procedures depended on the use of heparin to prevent fatal blood clotting. Heparin then came into standard use, although it does carry a possible risk of excessive bleeding.

Coumarin and Warfarin

Oral anticoagulants have their origins in an odd bleeding disorder in cattle that broke out in North Dakota and Canada in the 1920s. Cattle in these areas that ate hay made from spoiled sweet clover had a tendency to bleed to death. F. W. Schofield, a Canadian veterinarian, traced the deaths to clover in 1922. In 1931 a North Dakota veterinarian, L. M. Roderick, found that the hemorrhaging was caused by the reduced activity of prothrombin, a clotting factor in blood. Isolating prothrombin proved to be very difficult, but it was finally accomplished in 1939 by Karl Link and H. A. Campbell of the University of Wisconsin agricultural college. The clotting factor in prothrombin turned out to be dicumarol, a coumarin (a fragrant organic substance often extracted from tonka beans) compound that had originally been synthesized in an impure form in 1903.

In 1948 a potent synthetic form of dicumarol was originally introduced as an extremely effective rodent (small mammals of the order Rodentia, which includes rats, squirrels, and beavers) poison called warfarin (named for the patent holder, Wisconsin Alumni Research Foundation). Although warfarin rapidly became very popular worldwide as a rat poison, medical practitioners hesitated to use it on patients because it seemed so toxic (poisonous). This viewpoint changed after a United States army recruit unsuccessfully attempted suicide in 1951 by taking massive doses of warfarin-based rat poison. Warfarin is now the most widely prescribed oral anticoagulant.

Recent Developments

Research from the 1970s to 1990s has shown that the common painkiller aspirin has anticoagulant properties. In fact, doctors have recommended it for preventing blood clots near the heart. Apirin's fairly narrow in its effectiveness, however, and does not work as well to prevent strokes, blood clots in the legs, or clotting during surgery. Unfortunately, in order to do their job, anticoagulants suppress the human body's natural clotting process, which is used to heal wounds. Those patients on anticoagulants must always beware of excessive bleeding while taking the medication.

[See also Artificial kidney ]

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anticoagulant

anticoagulant (ăn´tēkōăg´yələnt), any of several substances that inhibit blood clot formation (see blood clotting). Some anticoagulants, such as the coumarin derivatives bishydroxycoumarin (Dicumarol) and warfarin (Coumadin) inhibit synthesis of prothrombin, a clot-forming substance, and other clotting factors. The coumarin derivatives compete with vitamin K, which is a necessary substance in prothrombin formation (see vitamin). They are only effective after the body's existing supply of prothrombin is depleted. Another anticoagulant, heparin, is a polysaccharide (see carbohydrate) found naturally in many cells. It acts in several ways: by preventing prothrombin formation; by preventing formation of fibrin, another clotting substance; and by decreasing the availability of a third clotting factor, thrombin. Heparin is obtained by extracting it from animal tissues. Anticoagulants are used to treat blood clots, which appear especially frequently in veins of the legs and pelvis in bedridden patients. Therapy helps to reduce the risk of clots reaching the lung, heart, or other organs. Heparin causes an instantaneous increase in blood-clotting time, and its effect lasts several hours.

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anticoagulant

an·ti·co·ag·u·lant / ˌantēkōˈagyələnt; ˌantī-/ • adj. having the effect of retarding or inhibiting the coagulation of the blood. • n. an anticoagulant substance.

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anticoagulant

anticoagulant (anti-koh-ag-yoo-lănt) n. an agent, such as heparin or warfarin, that prevents the clotting of blood and is used in the treatment of such conditions as thrombosis and embolism. Incorrect dosage may result in haemorrhage.

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"anticoagulant." A Dictionary of Nursing. 2008. Encyclopedia.com. 28 May. 2016 <http://www.encyclopedia.com>.

"anticoagulant." A Dictionary of Nursing. 2008. Encyclopedia.com. (May 28, 2016). http://www.encyclopedia.com/doc/1O62-anticoagulant.html

"anticoagulant." A Dictionary of Nursing. 2008. Retrieved May 28, 2016 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O62-anticoagulant.html

anticoagulant

anticoagulant A substance that prevents the formation of blood clots. Heparin is a natural anticoagulant, which is extracted to treat such conditions as thrombosis and embolism. Synthetic anticoagulants include warfarin.

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"anticoagulant." A Dictionary of Biology. 2004. Encyclopedia.com. 28 May. 2016 <http://www.encyclopedia.com>.

"anticoagulant." A Dictionary of Biology. 2004. Encyclopedia.com. (May 28, 2016). http://www.encyclopedia.com/doc/1O6-anticoagulant.html

"anticoagulant." A Dictionary of Biology. 2004. Retrieved May 28, 2016 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O6-anticoagulant.html

anticoagulant

anticoagulant A substance that inhibits the clotting of blood.

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MICHAEL ALLABY. "anticoagulant." A Dictionary of Zoology. 1999. Encyclopedia.com. 28 May. 2016 <http://www.encyclopedia.com>.

MICHAEL ALLABY. "anticoagulant." A Dictionary of Zoology. 1999. Encyclopedia.com. (May 28, 2016). http://www.encyclopedia.com/doc/1O8-anticoagulant.html

MICHAEL ALLABY. "anticoagulant." A Dictionary of Zoology. 1999. Retrieved May 28, 2016 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O8-anticoagulant.html

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