Acyclovir is widely used in the treatment of herpes virus infections, including herpes simplex virus (HSV) types 1 and 2, as well as varicella-zoster virus (VZV). It is effective in managing genital herpes, cold sores, shingles, and chickenpox. The medication works by inhibiting viral DNA replication, thereby reducing the severity and duration of outbreaks. It is also used as a preventive measure to suppress recurrent infections in immunocompromised patients, such as those with HIV or undergoing chemotherapy. Additionally, acyclovir is administered to prevent herpes infections in organ transplant recipients. Topical formulations are available for localized treatment of herpes labialis and genital herpes lesions.