Acycloguanosine is a synthetic base analog with the chemical formula of C8H11N5O3. It is mainly used for various infections caused by herpes simplex virus, and can be used for initial or recurrent skin, mucosa, external genital infection, and HSV infection in people with immune deficiency. It is the first choice drug for treating HSV encephalitis. It is better than adenosine arabinoside in reducing incidence rate and mortality. It can also be used for herpes zoster, EB virus, and varicella in people with immune deficiency.