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Pharmacology: Pharmacodynamics: Acyclovir is an antiviral agent which is highly active in vitro against Herpes simplex virus (HSV) type I and II and Varicella zoster virus. Toxicity to mammalian host cells is low.
Acyclovir is phosphorylated after entry into herpes infected cells to the active compound acyclovir triphosphate. The first step in the process is dependent on the presence of the HSV coded thymidine kinase. Acyclovir triphosphate acts as an inhibitor of and substrate for the herpes specified DNA polymerase preventing further viral DNA synthesis with affecting normal cellular processes.
Pharmacokinetics: Percutaneous absorption of Acyclovir appears to be minimal following topical application of the drug to intact skin. The distribution of Acyclovir following topical application has not been determined. In vitro Acyclovir appears to be preferentially distributed into cells that are infected with herpesviruses. In vitro Acyclovir is metabolized in cells infected with herpesviruses, principally by intracellular phosphorylation of the drug by virus-coded thymidine kinase and several cellular enzymes. Following systemic absorption, Acyclovir is excreted principally in urine 0.04% of the daily dose.
