Acyclovir, also known as acyclovir, is an antiviral drug of guanine analogues. Acyclovir is one of the most commonly used antiviral drugs, mainly used in the treatment of herpes simplex virus infection, but also for the treatment of herpes zoster. Acyclovir was once regarded as the beginning of a new era of antiviral therapy because of its high selectivity and low cytotoxicity. Its inventor Gertrude B. elien, an American pharmacologist, also won the Nobel Prize in physiology or medicine in 1988.