Aciclovir (INN) or acyclovir (USAN, former BAN), chemical name acycloguanosine, abbreviated as ACV, is a guanosine analogue antiviral drug, marketed under trade names such as Cyclovir, Herpex, Acivir, Acivirax, Zovirax, and Xovir. One of the most commonly used antiviral drugs, it is primarily used for the treatment of herpes simplex virus infections, as well as in the treatment of varicella zoster (chickenpox) and herpes zoster (shingles).