NCIt definition : A synthetic acyclic guanine derivative with antiviral activity, mainly used to treat
infections from herpes simplex virus (HSV) types 1 and 2. In HSV infected cells, penciclovir
is phosphorylated by viral thymidine kinase and subsequently converted by cellular
kinases into the active metabolite, penciclovir triphosphate, which competitively
inhibits viral HSV polymerase by blocking deoxyguanosine triphosphate substrate binding.
As a result, herpes viral DNA synthesis and replication are selectively inhibited.;