Acyclovir and valaciclovir belong to the group of nucleoside inhibitors of herpes viruses. Acyclovir is converted in the cell into active acyclovir triphosphate by the viral enzyme thymidine kinase. The triphosphate form competitively inhibits the viral DNA polymerase. This leads to a blockade of the viral DNA synthesis and thus of the viral replication.
Acyclovir has excellent oral absorption.
Extra info: Despite having poor bioavailability, acyclovir is rarely given by i.v. injection.
Acyclovir inhibits HSV and varicella zoster virus.
Acyclovir inactivates the viral DNA polymerase in an irreversible way.
Extra info: Acyclovir blocks the DNA synthesis by replacing guanosine. So, when acyclovir is taken away, normal DNA synthesis can go on.