famciclovir [ 9-(4-acetoxy-3-(acetoxymethyl)but-1-yl)-2-aminopurine,BRL 42810,BRL-42810,Famvir ] prodrug of penciclovir; phosphorylated by viral thymidine kinase and subsequently cellular kinases to a penciclovir triphosphate, which inhibits herpes simplex 2 DNA polymerase in a competitive manner