acyclovir + penciclovir

Acyclovir and penciclovir are both synthetic acyclic guanine derivative antivirals used to treat herpes simplex virus (HSV) infections. Both drugs have a similar mechanism of action - they are selectively phosphorylated by viral thymidine kinase in infected cells, and their triphosphate forms inhibit viral DNA polymerase by competing with deoxyguanosine triphosphate, thereby inhibiting viral DNA synthesis and replication. Key differences between the two drugs include: - Penciclovir has a higher affinity for HSV thymidine kinase than acyclovir - Penciclovir triphosphate has a longer intracellular half-life (10-20 hours) compared to acyclovir triphosphate (0.7-1 hour) - Acyclovir triphosphate is an obligate DNA chain terminator, while penciclovir triphosphate allows limited DNA chain elongation (short-chain terminator) While these drugs are not typically administered together as a fixed combination, they represent two important antiviral options for treating herpes infections.