After oral administration, Valacyclovir HCI is rapidly absorbed from the gastrointestinal tract and nearly completely converted to Acyclovir and L-valine by first-pass intestinal and/or hepatic metabolism. Acyclovir is a synthetic purine nucleoside analog that possesses in vitro and in vivo inhibitory against Herpes simplex virus type 1 (HSV-1 ), type 2 (HSV-2), and Varicella - zoster virus (VZV). Acyclovir activated by herpes virus thymidine kinase which result in phosphorylation to produce Acyclovir triphosphate, the active form of the Acyclovir. Acyclovir triphosphate is achieved by the prevention of viral DNA replication. Viral DNA replication is prevented through three mechanisms: competitive inhibition of viral DNA polymerase, incorporation into and termination of the growing viral DNA chain, and inactivation of viral DNA polymerase.
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