Purine nucleosides

Purine nucleosides are antiviral agents that have selective activity against herpes simplex virus types 1 (cold sores) and 2 (genital herpes) and varicella zoster virus (chicken pox).

The purine nucleoside molecule is converted to a monophosphate by viral thymidine kinases. The monophosphate is then converted to diphosphate and then into a triphosphate form by cellular enzymes. The triphosphate form blocks the replication of viral DNA by inhibiting viral DNA polymerase and terminating the growing viral DNA chain.

Purine nucleosides are more potent against the viral enzymes than the host enzymes.