Used primarily to treat infections caused by herpes viruses, including genital herpes, cold sores (herpes labialis), and shingles (herpes zoster). It is also used in the management of chickenpox (varicella) in certain patients. Acyclovir works by inhibiting viral DNA replication, thereby reducing the severity and duration of symptoms. It is available in oral, topical, and intravenous forms, making it suitable for mild to severe infections. In immunocompromised patients, such as those undergoing chemotherapy or with HIV, acyclovir is often used prophylactically to prevent herpes outbreaks.