Acyclovir competitively inhibits viral DNA polymerase by acting as an analog to deoxyguanosine triphosphate (dGTP). Incorporation of acyclovir into DNA results in chain termination since the absence of a 3' hydroxyl group prevents the attachment of additional nucleosides. Acyclovir is used to treat the symptoms of chickenpox, shingles, herpes virus infections of the genitals (sex organs), the skin, the brain, and mucous membranes (lips and mouth), and widespread herpes virus infections in newborns.