<p>Famciclovir rapidly undergoes biotransformation to penciclovir, which has inhibitory activity against HSV types 1 (HSV-1) and 2 (HSV-2), varicella-zoster virus (VZV). Thymidine kinase then phosphorylates penciclovir to a monophosphate form, which is then converted to penciclovir triphosphate. This inhibits HSV-2 DNA polymerase by competing with deoxyguanosine triphosphate, thus inhibiting herpes viral DNA synthesis and replication.</p>