Famciclovir is the well-absorbed oral form of penciclovir, an antiviral agent with potent activity against varicella-zoster virus (VZV) and herpes simplex virus (HSV-1) and 2 (HSV-2). After oral administration, famciclovir is rapidly converted to penciclovir with a bioavailability of 77%. penciclovir is efficiently phosphorylated to the active metabolite, penciclovir-triphosphate, and has a prolonged intracellular half-life of approximately 9-10 h in VZV-infected cells, and 10 and 20 h in cells infected with HSV-1 and HSV-2, respectively. Two multicenter clinical trials have shown that famciclovir given during the acute zoster phase accelerated healing of cutaneous lesions. More importantly, in a placebo-controlled study, famciclovir reduced the duration of postherpetic neuralgia (PHN), particularly in elderly patients. Famciclovir has also been proven effective in treating recurrent genital herpes, as demonstrated by a reduction in times to cessation of viral shedding, complete healing, and loss of all symptoms. One study showed that suppressive therapy with famciclovir was effective in reducing genital herpes episodes in patients with frequent recurrences. A promising new area of investigation for famciclovir is controlling virus replication in patients with chronic hepatitis B virus (HBV) or HBV reinfections after liver transplant. Results from a double-blind, placebo-controlled, pilot study and several case reports have shown that famciclovir, alone or in combination with other agents, decreased HBV-DNA levels and was tolerated with long-term treatment. Available clinical data indicate that famciclovir is an effective agent for treating herpes and holds significant promise for the treatment of chronic HBV infection HBV reinfection after liver transplantation.