Acyclovir

Acyclovir, an acyclic guanine nucleoside analog developed by Elion and Hitchings, is an antiherpesvirus agent like penciclovir [P2164]. Valacyclovir [V0111] is a prodrug of acyclovir. Acyclovir 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 acyclovir, which has extremely low toxicity for human cell. The spectrum of activity of acyclovir against human herpesviruses is similar to that of penciclovir, 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 penciclovir, acyclovir has slight activity against cytomegalovirus (CMV).