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Antiviral Drugs

Antiviral drugs

Definition

Antiviral drugs act against diseases caused by viruses.

Description

Viruses represent a large group of infective agents that are composed of a core of nucleic acids, either RNA or DNA, surrounded by a layer of protein. They are not really living organisms according to general understanding, since they lack the cell membrane that is associated with living cells. Viruses can reproduce only inside a living cell, and they cause many diseases. Viruses are not normally affected by antibiotics but a small number of viruses can either be destroyed or have their growth stopped by drugs.

The drugs as of 2004 available for treatment of viral diseases in children are:

  • Acyclovir (Zovirax), used for treatment of diseases caused by the erpes simplex virus and herpes zoster virus. Although it is approved only for children over the age of six months, the drug has been used for newborn infants with encephalitis . This drug is most reliable when given intravenously.
  • Amantidine (Symmetrel), used to prevent or treat infections of the influenza virus type A. It is recommended for patients who cannot or should not receive influenza virus vaccine. As of 2004 it has not been studied in children below the age of one year.
  • Foscarnet (Foscavir), is not recommended for young children but may be given to adolescents. It is used to treat cytomegalovirus infections of the eye, and for herpes simplex infections that are resistant to other drugs.
  • Ganciclovir (Cytovene), used to treat cytomegalovirus infections of the eye. Although the manufacturer does not recommend use of ganciclovir in patients below the age of 12 years, the drug is recommended by standard pediatric references for children as young as three months.
  • Oseltamivir (Tamiflu), used for treatment of influenza virus infections of children over the age of 13 years. In adults, oseltamivir has also been used for prevention if influenza, but this use has not been studied in children.
  • Ribavirin (Rebetol, Virazol), used for treatment of hospitalized infants and young children with severe lower respiratory tract infections caused by respiratory syncytial virus (RSV), but its value is controversial.
  • Rimantidine (Flumadine), used to protect against the influenza virus type A.
  • Valacyclovir (Valtrex), used for treatment of diseases caused by the herpes simplex virus and herpes zoster virus. This drug is converted to acyclovir inside the body and is more reliable for oral use. Although the manufacturer says that safety and efficacy in children have not been established, valacyclovir is recommended for use in standard pediatric resources.
  • Vidarabine (Vira-A), used to treat severe herpes infections in the newborn, but its primary value is in the form of an eye ointment to treat herpes infections of the eye.
  • Zanamivir (relenza), used to treat influenza infections caused by viruses types A and B in adults and children over the age of seven.

In addition to the above drugs, there are drugs which treat retrovirus infections. Retroviruses are composed of RNA molecules instead of DNA, and the only treatable one is the one that causes acquired immune deficiency syndrome (AIDS ). The drugs in this group that are appropriate for treatment of children are as follows:

  • abacavir (Ziagen)
  • amprenavir (Agenerase), for children above the age of four
  • didanosine (Videx)
  • efavirenz (Sustiva), for children over the age of three
  • indinavir (Crixavan), according to the manufacturer safety and efficacy of which in children has not been established, but the drug has been recommended in standard pediatric references
  • lamivudine (Epivir), for treatment of hepatitis B as well as for AIDS
  • lopinavir/Ritonavir fixed combination (Kaletra), used in children as young as six months
  • stavudine (Zerit)
  • nelfinavir (Viracept), the manufacturer of which does not recommend use of this drug for children younger than two, but it has been studied with some success in children as young as newborns
  • ritonavir (Norvir)
  • saquinavir (Fortovase, Invirase)
  • zalcitabine (Hivid)
  • zidovudine (Retrovir)

Other drugs for treatment of HIV disease are marketed, but there have been neither sufficient studies not clinical experience to recommend their use in children.

General use

The antiviral drugs are used to prevent or treat the diseases listed above. These drugs are specific for individual viruses and offer no benefit for conditions caused by other viruses.

Precautions

Each of the drugs listed has specific warnings. See specific drugs references or ask a pediatrician.

Side effects

Each of the drugs listed has its own side effects. See specific drugs references or ask a pediatrician.

Indinavir (Crixivan) has the unique adverse effects of causing changes in patterns of fat distribution. This has been called Crix belly and may be more distressing to the patient than more serious side effects caused by other drugs since these effects are clearly visible. As of 2004 it is not clear whether this effect can be reversed when the drug is discontinued. Antiretroviral drugs should not be discontinued unless there is an alternative antiretroviral regimen to adopt.

Interactions

See specific drugs references or ask a pediatrician about interactions for an antiviral drug that has been prescribed.

Patients should use these drugs exactly as directed. With regard to the AIDS drugs in particular, the drugs should not be discontinued without consultation with the prescriber. AIDS drugs are normally prescribed in combinations of two and three drugs used together, and discontinuing any single drug may lead to the virus developing resistance to the other agents.

Parental concerns

Liquid dosage forms must always be measured with a calibrated teaspoon or dropper, never with a household teaspoon. Household teaspoons vary in the volume they deliver and may result in inadvertent overdose or under dose.

Anti-influenza drugs should be used only for patients who cannot receive vaccinations. Annual vaccination remains the preferred method of preventing influenza.

Antiretroviral drugs are routinely given in combinations of three to four drugs at a time. In some cases, fixed combinations of medications are the most practical way to administer these drugs, since they require the lowest number of doses each day.

Some antiviral drugs, particularly the antiretroviral agents, have potentially severe adverse effects. They should be prescribed only by qualified professionals experienced in their use. These drugs must be routinely monitored. Regular laboratory testing is essential for safe and effective use. Adverse effects and side effects must be reported to the prescriber as soon as they are observed.

Antiherpetic drugs may have only a limited value in reducing the severity or duration of herpes attacks. They are more important for their effect in reducing the period of viral shedding, the period of time in which a person infected with herpes virus can infect other people. For this reason, continued use of the drugs is important to family members and those in close proximity to the patient. The drugs should not be discontinued, even if there is no observed benefit.

KEY TERMS

Herpes virus A family of viruses including herpes simplex types 1 and 2, and herpes zoster (also called varicella zoster). Herpes viruses cause several infections, all characterized by blisters and ulcers, including chickenpox, shingles, genital herpes, and cold sores or fever blisters.

Influenza virus type The nature of the proteins in the outer coat of an influenza virus. Depending on the proteins, influenza viruses may be classified as A, B, or C.

Retrovirus A family of RNA viruses containing a reverse transcriptase enzyme that allows the viruses' genetic information to become part of the genetic information of the host cell upon replication. Human immunodeficiency virus (HIV) is a retrovirus.

Virus A small infectious agent consisting of a core of genetic material (DNA or RNA) surrounded by a shell of protein. A virus needs a living cell to reproduce.

See also Herpes simplex; HIV infection and AIDS; Influenza.

Resources

BOOKS

Beers, Mark H., and Robert Berkow, eds. The Merck Manual, 2nd home ed. West Point, PA: Merck & Co., 2004.

Mcevoy, Gerald, et al. AHFS Drug Information 2004. Bethesda, MD: American Society of Healthsystems Pharmacists, 2004.

PERIODICALS

Bell, G. S. "Highly active antiretroviral therapy in neonates and young infants." Neonatal Netword: The Journal of Neonatal Nursing 23, no. 2 (March-April 2004: 5564.

Eksborg, S. "The pharmacokinetics of antiviral therapy in pediatric patients." Herpes 10, no. 3 (December 2003): 6671.

Fraaij, Pieter L., et al. "Therapeutic drug monitoring in children with HIV/AIDS." Therapeutic Drug Monitoring 26, no. 2 (April 2004): 1226.

Feder, Henry M., Jr., and Diane M. Hoss. "Herpes zoster in otherwise healthy children." Pediatric Infectious Diseases Journal 23, no. 5 (May 2004): 4517.

Jaspan, H. B., and R. F. Garry. "Preventing neonatal HIV: a review." Current HIV Research 1, no. 3 (July 2003): 3217.

Kamin, D., and C. Hadigan C. "Hyperlipidemia in children with HIV infection: an emerging problem." Expert Reviews in Cardiovascular Therapy 1, no. 1 (May 2003): 14350.

Maggon, Krishan, and Sailen Barik. "New drugs and treatment for respiratory syncytial virus." Reviews in Medical Virology 14, no. 3 (May-June 2004): 14968.

Rakhmanina, Natella Y., et al. "Therapeutic drug monitoring of antiretroviral therapy." AIDS Patient Care and STDS 18, no. 1 (January 2004): 714.

Whitley, Richard. "Neonatal herpes simplex virus infection." Current Opinion in Infectious Diseases 17, no. 3 (June 2004): 2436.

ORGANIZATIONS

Elisabeth Glaser Pediatric AIDS Foundation. 1140 Connecticut Avenue NW, Suite 200, Washington, DC 20036. Web site: <www.charitywire.com/charity60/>.

WEB SITES

National Institute of Allergy and Infectious Diseases. Available online at <www.niaid.nih.gov/default.htm> (accessed October 17, 2004).

National Institute of Child Health & Human Development. Available online at <www.nichd.nih.gov/> (accessed October 17, 2004).

National Pediatric AIDS Network. Available online at <www.npan.org/> (accessed October 17, 2004).

The Pediatric AIDS Clinical Trials Group. Available online at <http://pactg.s-3.com/> (accessed October 17, 2004)

"Pediatric Antiretroviral Drug Information." Available online at <http://aidsinfo.nih.gov/guidelines/pediatric%5CSUP_PED_012004.html> (accessed October 17, 2004).

Samuel Uretsky, PharmD

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"Antiviral Drugs." Gale Encyclopedia of Children's Health: Infancy through Adolescence. . Encyclopedia.com. 16 Dec. 2017 <http://www.encyclopedia.com>.

"Antiviral Drugs." Gale Encyclopedia of Children's Health: Infancy through Adolescence. . Encyclopedia.com. (December 16, 2017). http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/antiviral-drugs

"Antiviral Drugs." Gale Encyclopedia of Children's Health: Infancy through Adolescence. . Retrieved December 16, 2017 from Encyclopedia.com: http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/antiviral-drugs

Antiviral Drugs

Antiviral Drugs

Definition

Antiviral drugs are medicines that cure or control virus infections.

Purpose

Antivirals are used to treat infections caused by viruses. Unlike antibacterial drugs, which may cover a wide range of pathogens, antiviral agents tend to be narrow in spectrum, and have limited efficacy.

Description

Exclusive of the antiretroviral agents used in HIV (AIDS) therapy, there are currently only 11 antiviral drugs available, covering four types of virus. Acyclovir (Zovirax), famciclovir (Famvir), and valacyclovir (Valtrex) are effective against herpesvirus, including herpes zoster and herpes genitalis. They may also be of value in either conditions caused by herpes, such as chickenpox and shingles. These drugs are not curative, but may reduce the pain of a herpes outbreak and shorten the period of viral shedding.

Amantadine (Symmetrel), oseltamivir (Tamiflu), rimantidine (Flumadine), and zanamivir (Relenza) are useful in treatment of influenza virus. Amantadine, rimantadine, and oseltamivir may be administered throughout the flu season as preventatives for patients who cannot take influenza virus vaccine.

KEY TERMS

Asthenia Muscle weakness.

Cytomegalovirus (CMV) A type of virus that attacks and enlarges certain cells in the body. The virus also causes a disease in infants.

Herpes simplex A virus that causes sores on the lips (cold sores) or on the genitals (genital herpes).

HIV Acronym for human immunodeficiency virus, the virus that causes AIDS.

Parkinsonism A group of conditions that all have these typical symptoms in common: tremor, rigidity, slow movement, and poor balance and coordination.

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.

Prophylactic Guarding from or preventing the spread or occurrence of disease or infection.

Retrovirus A group of viruses that contain RNA and the enzyme reverse transcriptase. Many viruses in this family cause tumors. The virus that causes AIDS is a retrovirus.

Shingles An disease caused by an infection with the Herpes zoster virus, the same virus that causes chickenpox. Symptoms of shingles include pain and blisters along one nerve, usually on the face, chest, stomach, or back.

Virus A tiny, disease-causing structure that can reproduce only in living cells and causes a variety of infectious diseases.

Cidofovir (Vistide), foscarnet (Foscavir), and ganciclovir (Cytovene) have been beneficial in treatment of cytomegalovirus in immunosupressed patients, primarily HIV-positive patients and transplant recipients. Ribavirin (Virazole) is used to treat respiratory syncytial virus. In combination with interferons, ribavirin has shown some efficacy against hepatitis C, and there have been anecdotal reports of utility against other types of viral infections.

As a class, the antivirals are not curative, and must be used either prophylactically or early in the development of an infection. Their mechanism of action is typically to inactivate the enzymes needed for viral replication. This will reduce the rate of viral growth, but will not inactive the virus already present. Antiviral therapy must normally be initiated within 48 hours of the onset of an infection to provide any benefit. Drugs used for influenza may be used throughout the influenza season in high risk patients, or within 48 hours of exposure to a known carrier. Antiherpetic agents should be used at the first signs of an outbreak. Anti-cytomegaloviral drugs must routinely be used as part of a program of secondary prophylaxis (maintenance therapy following an initial response) in order to prevent reinfection in immunocompromised patients.

Recommended dosage

Dosage varies with the drug, patient age and condition, route of administration, and other factors. See specific references.

Precautions

Ganciclovir is available in intravenous injection, oral capsules, and intraoccular inserts. The capsules should be reserved for prophylactic use in organ transplant patients, or for HIV infected patients who cannot be treated with the intravenous drug. The toxicity profile of this drug when administered systemically includes granulocytopenia, anemia and thrombocytopenia. The drug is in pregnancy category C, but has caused significant fetal abnormalities in animal studies including cleft palate and organ defects. Breast feeding is not recommended.

Cidofovir causes renal toxicity in 53% of patients. Patients should be well hydrated, and renal function should be checked regularly. Other common adverse effects are nausea and vomiting in 65% or patients, asthenia in 46% and headache and diarrhea, both reported in 27% of cases. The drug is category C in pregnancy, due to fetal abnormalities in animal studies. Breast feeding is not recommended.

Foscarnet is used in treatment of immunocompromised patients with cytomegalovirus infections and in acyclovir-resistant herpes simples virus. The primary hazard is renal toxicity. Alterations in electrolyte levels may cause seizures. Foscarnet is category C during pregnancy. The drug has caused skeletal abnormailities in developing fetuses. It is not known whether foscarnet is excreted in breast milk, however the drug does appear in breast milk in animal studies.

Valaciclovir is metabolized to acyclovir, so that the hazards of the two drugs are very similar. They are generally well tolerated, but nausea and headache are common adverse effects. They are both pregnancy category B. Although there have been no reports of fetal abnormalities attributable to either drug, the small number of reported cases makes it impossible to draw conclusions regarding safety in pregnancy. Acyclovir is found in breast milk, but no adverse effects have been reported in the newborn. Famciclovir is similar in actions and adverse effects.

Ribavirin is used by aerosol for treatment of hospitalized infants and young children with severe lower respiratory tract infections due to respiratory syncytial virus (RSV). When administered orally, the drug has been used in adultys to treat other viral diseases including acute and chronic hepatitis, herpes genitalis, measles, and Lassa fever, however there is relatively little information about these uses. In rare cases, initiation of ribavirin therapy has led to deterioration of respiratory function in infants. Careful monitoring is essential for safe use.

The anti-influenza drugs are generally well tolerated. Amantadine, which is also used for treatment of Parkinsonism, may show more frequent CNS effects, including sedation and dizziness. Rapid discontinuation of amantidine may cause an increase in Parkinsonian symptoms in patients using the drug for that purpose. All are schedule C for pregnancy. In animal studies, they have caused fetal malformations in doses several times higher than the normal human dose. Use caution in breast feeding.

Interactions

Consult specific references for information on drug interactions.

Use particular caution in HIV-positive patients, since these patients are commonly on multi-drug regimens with a high frequency of interactions. Ganciclovir should not be used with other drugs which cause hematologic toxicity, and cidofovir should not be used with other drugs that may cause kidney damage.

Resources

PERIODICALS

Gray, Mary Ann. "Antiviral Medications." Orthopaedic Nursing 15 (November-December 1996): 82.

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"Antiviral Drugs." Gale Encyclopedia of Medicine, 3rd ed.. . Encyclopedia.com. 16 Dec. 2017 <http://www.encyclopedia.com>.

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"Antiviral Drugs." Gale Encyclopedia of Medicine, 3rd ed.. . Retrieved December 16, 2017 from Encyclopedia.com: http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/antiviral-drugs-0

Antiviral Drugs

Antiviral drugs

Definition

Antiviral drugs are medicines that cure or control virus infections.

Purpose

Antivirals are used to treat infections caused by viruses. Unlike antibacterial drugs, which may cover a wide range of pathogens, antiviral agents tend to be narrow in spectrum, and have limited efficacy.

Description

Exclusive of the antiretroviral agents used in HIV (AIDS ) therapy, there are currently only 11 antiviral drugs available, covering four types of virus. Acyclovir (Zovirax), famciclovir (Famvir), and valacyclovir (Valtrex) are effective against the herpes virus, including herpes zoster and herpes genitalis. They may also be of value in either conditions caused by herpes, such as chicken pox and shingles . These drugs are not curative, but may reduce the pain of a herpes outbreak and shorten the period of viral shedding.

Amantadine (Symmetrel), oseltamivir (Tamiflu), rimantidine (Flumadine), and zanamivir (Relenza) are useful in treatment of the influenza virus. Amantadine, rimantadine, and oseltamivir may be administered throughout the flu season as preventatives for patients who cannot take influenza virus vaccine.

Cidofovir (Vistide), foscarnet (Foscavir), and ganciclovir (Cytovene) have been beneficial in treatment of cytomegalovirus in immunosupressed patients, primarily HIV-positive patients and transplant recipients. Ribavirin (Virazole) is used to treat respiratory syncytial virus. In combination with interferons , ribavirin has shown some efficacy against hepatitis C, and there have been anecdotal reports of utility against other types of viral infections.

As a class, the antivirals are not curative, and must be used either prophylactically or early in the development of an infection. Their mechanism of action is typically to inactivate the enzymes needed for viral replication. This will reduce the rate of viral growth, but will not inactive the virus already present. Antiviral therapy must normally be initiated within 48 hours of the onset of an infection to provide any benefit. Drugs used for influenza may be used throughout the influenza season in high risk patients, or within 48 hours of exposure to a known carrier. Antiherpetic agents should be used at the first signs of an outbreak. Anti-cytomegaloviral drugs must routinely be used as part of a program of secondary prophylaxis (maintenance therapy following an initial response) in order to prevent reinfection in immunocompromised patients.

Recommended dosage

Dosage varies with the drug, patient age and condition, route of administration, and other factors. See specific references.

Precautions

Ganciclovir is available in intravenous injection, oral capsules, and intraoccular inserts. The capsules should be reserved for prophylactic use in organ transplant patients, or for HIV infected patients who cannot be treated with the intravenous drug. The toxicity profile of this drug when administered systemically includes granulocytopenia, anemia, and thrombocytopenia. The drug is in pregnancy category C, but has caused significant fetal abnormalities in animal studies including cleft palate and organ defects. Breast-feeding is not recommended.

Cidofovir causes renal toxicity in 53% of patients. Patients should be well hydrated, and renal function should be checked regularly. Other common adverse effects are nausea and vomiting in 65% or patients, asthenia in 46% and headache and diarrhea, both reported in 27% of cases. The drug is category C in pregnancy, due to fetal abnormalities in animal studies. Breast-feeding is not recommended.

Foscarnet is used in treatment of immunocompromised patients with cytomegalovirus infections and in acyclovir-resistant herpes simples virus. The primary hazard is renal toxicity. Alterations in electrolyte levels may cause seizures . Foscarnet is category C during pregnancy. The drug has caused skeletal abnormalities in developing fetuses. It is not known whether foscarnet is excreted in breast milk, however the drug does appear in breast milk in animal studies.

Valaciclovir is metabolized to acyclovir, so that the hazards of the two drugs are very similar. They are generally well tolerated, but nausea and headache are common adverse effects. They are both pregnancy category B. Although there have been no reports of fetal abnormalities attributable to either drug, the small number of reported cases makes it impossible to draw conclusions regarding safety in pregnancy. Acyclovir is found in breast milk, but no adverse effects have been reported in the newborn. Famciclovir is similar in actions and adverse effects.

Ribavirin is used by aerosol for treatment of hospitalized infants and young children with severe lower respiratory tract infections due to respiratory syncytial virus (RSV). When administered orally, the drug has been used in adults to treat other viral diseases including acute and chronic hepatitis, herpes genitalis, measles, and Lassa fever, however there is relatively little information about these uses. In rare cases, initiation of ribavirin therapy has led to deterioration of respiratory function in infants. Careful monitoring is essential for safe use.

The anti-influenza drugs are generally well tolerated. Amantadine, which is also used for treatment of Parkinsonism, may show more frequent CNS effects, including sedation and dizziness . Rapid discontinuation of amanti-dine may cause an increase in Parkinsonian symptoms in patients using the drug for that purpose. All are schedule C for pregnancy. In animal studies, they have caused fetal malformations in doses several times higher than the normal human dose. Use caution in breast-feeding.

Interactions

Consult specific references for information on drug interactions.

Use particular caution in HIV-positive patients, since these patients are commonly on multi-drug regimens with a high frequency of interactions. Ganciclovir should not be used with other drugs which cause hematologic toxicity, and cidofovir should not be used with other drugs that may cause kidney damage.

Resources

PERIODICALS

Gray, Mary Ann. "Antiviral Medications." Orthopaedic Nursing 15 (November-December 1996): 82.

Samuel D. Uretsky, PharmD

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Antiviral Drugs

Antiviral drugs

Antiviral drugs are compounds that are used to prevent or treat viral infections, via the disruption of an infectious mechanism used by the virus, or to treat the symptoms of an infection.

Different types of antiviral drugs have different modes of operation. For example, acyclovir is a drug that is used to treat the symptoms of the infections arising from the herpes virus family. Such infection includes lesions on the genitals, oral region, or in the brain. Acyclovir is also an antiviral agent in the treatment of chickenpox in children and adults, and shingles in adults caused by the reactivation of the chickenpox virus after a period of latency. Shingles symptoms can also be treated by the administration of valacyclovir and famciclovir.

Eye infections caused by cytomegalovirus can be treated with the antiviral agent known as ganciclovir. The drug acts to lessen the further development and discomfort of the eye irritation. But, the drug may be used as a preventative agent in those people whose immune system will be compromised by the use of an immunosupressant.

Another category of antiviral drugs is known as the antiretroviral drugs. These drugs target those viruses of clinical significance called retroviruses that use the mechanism of reverse transcription to manufacture the genetic material needed for their replication. The prime example of a retrovirus is the Human immunodeficiency virus (HIV ), which is the viral agent of acquired immunodeficiency syndrome (AIDS ). The development of antiviral drugs has been stimulated by the efforts to combat HIV. Some anti-HIV drugs have shown promise against hepatitis B virus, herpes simplex virus, and varicella-zoster virus.

The various antiviral agents are designed to thwart the replication of whatever virus they are directed against. One means to achieve this is by blocking the virus from commandeering the host cell's nuclear replication machinery in order to have its genetic material replicated along with the host's genetic material. The virus is not killed directly. But the prevention of replication will prevent the numbers of viruses from increasing, giving the host's immune system time to deal with the stranded viruses.

The incorporation of the nucleotide building blocks into deoxyribonucleic acid (DNA ) can be blocked using the drug idoxuridine or trifluridine. Both drugs replace the nucleoside thymidine, and its incorporation produces a nonfunctional DNA. However, the same thing happens to the host DNA. So, this antiviral drug is also an anti-host drug. Vidarabine is another drug that acts in a similar fashion. The drug is incorporated into DNA in place of adenine. Other drugs that mimic other DNA building blocks.

Blockage of the viral replicative pathway by mimicking nucleosides can be successful. But, because the virus utilizes the host's genetic machinery, stopping the viral replication usually affects the host cell.

Another tact for antiviral drugs is to block a viral enzyme whose activity is crucial for replication of the viral genetic material. This approach has been successfully exploited by the drug acyclovir. The drug is converted in the host cell to a compound that can out compete another compound for the binding of the viral enzyme, DNA polymerase, which is responsible for building DNA. The incorporation of the acyclovir derivative exclusively into the viral DNA stops the formation of the DNA. Acyclovir has success against herpes simplex viruses, and Epstein-Barr virus . Another drug that acts in a similar fashion is famiciclovir.

Other antiviral drugs are directed at the translation process, whereby the information from the viral genome that has been made into a template is read to produce the protein product. For example, the drug ribavirin inhibits the formation of messenger ribonucleic acid .

Still other antiviral drugs are directed at earlier steps in the viral replication pathway. Amantadine and rimantadine block the influenza A virus from penetrating into the host cell and releasing the nuclear material.

Antiviral therapy also includes molecular approaches. The best example is the use of oligonucleotides. These are sequences of nucleotides that are specifically synthesized to be complimentary with a target sequence of viral ribonucleic acid. By binding to the viral RNA , the oligonucleotide blocks the RNA from being used as a template to manufacture protein.

The use of antiviral drugs is not without risk. Host cell damage and other adverse host reactions can occur. Thus, the use of antiviral drugs is routinely accompanied by close clinical observation.

See also Immunodeficiency diseases; Viruses and responses to viral infection

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antiviral drug

antiviral drug, any of several drugs used to treat viral infections. The drugs act by interfering with a virus's ability to enter a host cell and replicate itself with the host cell's DNA. Some drugs block the virus's attachment or entry into the cell; others inhibit replication or prevent the virus from shedding the protein coat that surrounds the viral DNA. Antiviral drug development has been concurrent with advances in molecular biology and genetic engineering that allow study and definition of the genetic codes of viral DNA. Study at this level was not possible until electron microscopes became available and it is only since the 1980s that antiviral drugs have been on the market.

Antivirals are now available for a wide variety of viral diseases. Ribavirin, available since the mid-1980s, is used to treat respiratory syncytial virus (RSV), a cause of severe childhood respiratory infections. It is thought to inhibit messenger RNA. Ribavirin has few side effects, but is prohibitively expensive for all but the most serious cases. Amantadine and rimantadine, which are effective against strains of influenza A, act by interfering with viral uncoating.

Herpes simplex virus can now be treated by a highly selective drug, acyclovir (Zovirax), that interferes with an enzyme critical to the growth of the DNA chain. Although not a cure, the drug lessens the frequency and severity of outbreaks. Acyclovir is also used to lessen the pain and speed the healing of herpes zoster (shingles).

The search for cures and palliatives for AIDS has yielded drugs such as zidovudine (AZT), which inhibits the transcription of RNA to DNA in human immunodeficiency virus (HIV). Ganciclovir and cidofovir are used in the treatment of cytomegalovirus (CMV), a virus that affects the eyes of immunosuppressed patients. Fomivirsen, which is an antisense drug, is also used to treat CMV.

See also nucleic acid, virus, retrovirus.

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antiviral

antiviral Describing a drug or other agent that kills or inhibits viruses and is used to combat viral infections. Several types of antiviral drug are now in use, such as acyclovir, effective against herpesviruses, and zidovudine (AZT), a reverse transcriptase inhibitor that is used to treat HIV infection. The body's own natural antiviral agents, interferons, can now be produced by genetic engineering and are sometimes used therapeutically. However, many antiviral agents are extremely toxic, and viruses evolve rapidly so that a drug's effectiveness can soon be lost.

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"antiviral." A Dictionary of Biology. . Retrieved December 16, 2017 from Encyclopedia.com: http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/antiviral

antiviral drug

antiviral drug (anti-vy-răl) n. a drug effective against viruses that cause disease. Antiviral drugs include aciclovir, ganciclovir, foscarnet, oseltamivir, and ribavirin, used for treating herpes, cytomegalovirus, influenza, and respiratory syncytial virus infections; and antiretroviral drugs, used for treating HIV infections and AIDS.

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"antiviral drug." A Dictionary of Nursing. . Encyclopedia.com. 16 Dec. 2017 <http://www.encyclopedia.com>.

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"antiviral drug." A Dictionary of Nursing. . Retrieved December 16, 2017 from Encyclopedia.com: http://www.encyclopedia.com/caregiving/dictionaries-thesauruses-pictures-and-press-releases/antiviral-drug

antiviral

an·ti·vi·ral / ˌantēˈvīrəl; ˌantī-/ • adj. Med. (chiefly of a drug or treatment) effective against viruses.

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"antiviral." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. 16 Dec. 2017 <http://www.encyclopedia.com>.

"antiviral." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. (December 16, 2017). http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/antiviral

"antiviral." The Oxford Pocket Dictionary of Current English. . Retrieved December 16, 2017 from Encyclopedia.com: http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/antiviral