Famciclovir: a new systemic antiviral agent for herpesvirus infections.

Acyclovir was the first antiviral drug approved for the treatment of herpes zoster. Several new antiviral agents have since been introduced, one of which is famciclovir. The pharmacokinetics of famciclovir allow a more convenient dosing schedule than the schedule used with acyclovir. Famciclovir is metabolized in the liver, but the P450 cytochrome system is not involved. Both acyclovir and famciclovir accelerate cutaneous healing, but studies suggest that famciclovir may reduce the severity of postherpetic neuralgia when compared with placebo. Famciclovir is currently approved only for use in immunocompetent patients, but clinical trials involving immunocompromised patients are in progress.