Used primarily to treat viral infections caused by DNA viruses, particularly cytomegalovirus (CMV) in immunocompromised patients such as those with AIDS. It is effective in treating CMV retinitis when other treatments are not suitable or have failed. The drug is also investigated for use against other herpesviruses, adenoviruses, and poxviruses, including smallpox and monkeypox, due to its broad-spectrum antiviral activity. Topical formulations have been used off-label to treat recalcitrant cutaneous viral infections like warts caused by human papillomavirus (HPV). Its use is limited by potential kidney toxicity, requiring careful monitoring and probenecid co-administration to reduce risk.