The pharmacological profile of famciclovir

Famciclovir is the well-absorbed oral form of penciclovir, a potent and selective antiviral agent, with activity against members of the herpesvirus family, including varicella-zoster virus (VZV), and herpes simplex virus-1 (HSV-1) and HSV-2. Famciclovir is rapidly absorbed and converted to penciclovir. Penciclovir has excellent bioavailability (77%) after oral administration of 500 mg of famciclovir. Similar to acyclovir, famciclovir is converted by phosphorylation to its active metabolite, penciclovir-triphosphate. Penciclovir-triphosphate has a prolonged in vitro intracellular half-life of 10 to 20 hours in HSV-1-and HSV-2-infected cells, respectively, and 9 to 14 hours in VZV-infected cells. In contrast, the in vitro intracellular half-life of acyclovir is substantially shorter at 0.7 and 1 hours in HSV-1- and HSV-2-infected cells, respectively, and 0.8 hours in VZV-infected cells. Famciclovir is eliminated primarily via the kidneys. Dosage adjustment is not required for famciclovir in elderly patients with normal or mildly impaired renal function, and the extent of penciclovir availability is not affected by food. The excellent bioavailability ensures that adequate drug reaches virus-infected cells, and the prolonged intracellular half-life of the active form of famciclovir results in persistent antiviral activity.