Valacyclovir is the hydrochloride salt of the L-valyl ester of the antiviral drug acyclovir. Orally administered, valacyclovir is rapidly converted to acyclovir which inhibits viral DNA replication after further conversion to the nucleotide analog acyclovir triphosphate by viral thymidine kinase, cellular guanyl cyclase, and a number of other cellular enzymes. Valacyclovir is used to treat infections caused by certain types of viruses. In children, it is used to treat cold sores around the mouth (caused by herpes simplex) and chickenpox (caused by varicella zoster). In adults, it is used to treat shingles (caused by herpes zoster) and cold sores around the mouth. Valacyclovir is also used to treat outbreaks of genital herpes. In people with frequent outbreaks, this medication is used to reduce the number of future episodes. Valacyclovir is an antiviral drug it stops the growth of certain viruses.