Aciclovir is a synthetic purine nucleoside analogue with inhibitory activity against Herpes simplex viruses type 1 (HSV-1) and type 2 (HSV-2) in cell culture and in vivo. The inhibitory activity of Aciclovir is highly selective due to its affinity for the enzyme thymidine kinase (TK) encoded by HSV. This viral enzyme converts Aciclovir into Aciclovir monophosphate, a nucleotide analogue. The monophosphate is further converted into diphosphate by cellular guanylate kinase and into triphosphate by a number of cellular enzymes. In cell culture, Aciclovir Triphosphate stops replication of herpes viral DNA. This inhibition is accomplished in 3 ways: 1) competitive inhibition...