Vidarabine is primarily used as an antiviral medication, particularly in the treatment of infections caused by the herpes simplex virus and varicella-zoster virus. It is effective in managing conditions such as herpes simplex encephalitis, a severe infection of the brain, and herpes zoster (shingles) in immunocompromised patients. The compound works by inhibiting viral DNA synthesis, thereby reducing the replication of the virus. In ophthalmology, vidarabine is applied as an ophthalmic ointment to treat herpes simplex keratitis, an infection of the eye that can lead to blindness if untreated. Its use has declined with the advent of more effective antiviral agents, but it remains a valuable option in specific clinical scenarios. Use under medical supervision due to potential severe side effects.