Medical Health Encyclopedia

Nucleoside Analogues. The best class of drugs developed against varicella-zoster are those known as nucleoside, or guanosine, analogues, which are able to block viral reproduction. None of these agents can actually destroy the virus and cure the disease, but they can significantly reduce the severity of the attack, hasten healing, and reduce the duration. There is some evidence that early treatment (within 72 hours) with these agents can reduce the risk for postherpetic herpes.

Acyclovir (Zovirax), famciclovir (Famvir), and valaciclovir (Valtrex) are approved for shingles. Acyclovir is the oldest most studied of these drugs, but famciclovir (Famvir) or valaciclovir (Valtrex), which are both metabolized into acyclovir, are now preferred for herpes zoster for most patients. They relieve symptoms better than acyclovir and require fewer daily doses (typically three) than the five doses needed with acyclovir.

Because herpes zoster tends to resolve fairly quickly in young adults, these drugs are generally reserved for patients at greatest risk for complications or persistent pain. They include the following:

• Elderly people.
• Those with infections that threaten the eye.
• Patients who are HIV positive or immunocompromised in other ways.
• Patients whose infection covers a larger-than-average surface area of the skin.
• Those with very severe pain.

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Anti-viral agents are usually taken for seven days. Ideally they should be started within 72 hours of the onset of infection. The earlier they are given the more effective these agents are, but they can be helpful even if treatment is started after three days. Combinations of antiviral therapy with other drugs, such as tricyclic antidepressants or anti-seizure agents are under investigation.

These agents appear to have little or no harmful effect on healthy cells and can penetrate most body tissues, including cerebrospinal fluid. Evidence to date suggests that they are safe during pregnancy.