Penciclovir inhibits herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2), varicella-zoster virus (VZV), epstein-Barr virus (EBV), human cytomegalovirus (HCMV) with IC50 of 0.04-1.8 μg/mL, 0.06-4.4 μg/mL,1.6-8 μg/mL, 1.5-3.1 μg/mL, 51 μg/mL, respectively. Penciclovir (PCV) is an acyclic guanine derivative (which is not commercially available as an oral agent), has a spectrum of activity and a mechanism of action similar to those of acyclovir (ACV).