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.
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