Penciclovir is a guanine analogue antiviral drug used for the treatment of various herpesvirus infections. It is a nucleoside analogue which exhibits low toxicity and good selectivity. [Wikipedia] (en)
Penciclovir has <i>in vitro</i> activity against herpes simplex virus types 1 (HSV-1) and 2 (HSV-2). In cells infected with HSV-1 or HSV-2, viral thymidine kinase phosphorylates penciclovir to a monophosphate form. The monophosphate form of the drug is then converted to penciclovir triphosphate by cellular kinases. The intracellular triphosphate of penciclovir is retained <i>in vitro</i> inside HSV-infected cells for 10-20 hours, compared with 0.7-1 hour for acyclovir. <i>in vitro</i> studies show that penciclovir triphosphate selectively inhibits viral DNA polymerase by competing with deoxyguanosine triphosphate. Inhibition of DNA synthesis of virus-infected cells inhibits viral replication. In cells not infected with HSV, DNA synthesis is unaltered. Resistant mutants of HSV can occur from qualitative changes in viral thymidine kinase or DNA polymerase. The most commonly encountered acyclovir-resistant mutants that are deficient in viral thymidine kinase are also resistant to penciclovir. (en)
Measurable penciclovir concentrations were not detected in plasma or urine of healthy male volunteers (n= 12) following single or repeat application of the 1% cream at a dose of 180 mg penciclovir daily. (en)