Tremendous advances have been made over the past decade in the field of antiviral therapy. Acyclovir, which was commercially released about 10 years ago, is the therapeutic agent of choice for the treatment of herpes simplex and varicella-zoster infections. Acyclovir itself is not an active antiviral agent. When administered it is converted to the active, phosphorylated form of the drug by the action of virally coded thymidine kinase. The active form interferes with DNA polymerase and in so doing prevents viral replication. Host cells are relatively unaffected because they lack a thymidine kinase that can phosphorylate the parent acyclovir compound. Moreover, human cellular DNA polymerase is more resistant to drug effect than is viral DNA polymerase.
The adult dosage of orally administered acyclovir for the treatment of active herpes simplex infection is 200 mg 5 times/day. It is given for 10 days in primary infection and for 5 days in recurrent infection. For patients with chronic, frequently recurring, oral or genital herpes, the drug may be given continuously in a dosage of 200 mg 2 or 3 times/day. The Food and Drug Administration (FDA) has approved continuous therapy for up to 1 year, but studies have indicated that it can be given safely and effectively for appreciably longer periods of time.
Acyclovir is also effective, at appreciably higher dosage, in the treatment of varicella and herpes zoster (“shingles”). The adult dose for herpes zoster is 5OO mg (an 5OO-mg tablet is available) 5 times/day for 7 to 10 days. Although the symptoms and signs of zoster are ameliorated, acyclovir treatment has not yet been documented as effective in preventing the development of postherpetic neuralgia. Dosages and indications for use are just not being established for patients with varicella.
Side effects rarely occur with the use of orally administered acyclovir in the dosages. Resistance of the herpes viruses to acyclovir occurs with some frequency, but this has not represented a clinical problem, so fur at least, in immunocompetent patients.
Tags:food and drug administration fda, herpes simplex infection, herpes viruses, herpes zoster shingles, mg tablet therapeutic agent
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