Penciclovir

Penciclovir, an acyclic guanine nucleoside analog, is an antiherpesvirus agent like acyclovir [A1915] . Famciclovir [F0842] is a prodrug of penciclovir. Penciclovir is active against most species in the herpesvirus family. It depends on the activity of the viral enzyme thymidine kinase (TK) to convert the agent to a monophosphate form and subsequently interfere with viral DNA replication. In contrast, human cellular TK have very little ability to add the initial phosphate group to penciclovir, which has extremely low toxicity for human cell. The spectrum of activity of penciclovir against human herpesviruses is similar to that of acyclovir, both compounds having good activity against herpes simplex viruses types 1 and 2 (HSV-1, HSV-2), varicella-zoster virus (VZV), and Epstein-Barr virus (EBV). Like acyclovir, penciclovir has slight activity against cytomegalovirus (CMV).