Idoxuridine is an anti-herpesvirus antiviral drug. It is a nucleoside analogue, a modified form of deoxyuridine, similar enough to be incorporated into viral DNA replication, but the iodine atom added to the uracil component blocks base pairing. It is used only topically due to cardiotoxicity. Idoxuridine is mainly used topically to treat herpes simplex keratitis. Epithelial lesions, especially initial attacks presenting with a dendritic ulcer, are most responsive to therapy, while infection with stromal involvement are less responsive. Idoxuridine is ineffective against herpes simplex virus type 2 and varicella-zoster. Idoxuridine is mainly used topically to treat herpes simplex keratitis. Epithelial lesions, especially initial attacks presenting with a dendritic ulcer, are most responsive to therapy, while infection with stromal involvement are less responsive.[3] Idoxuridine is ineffective against herpes simplex virus type 2 and varicella-zoster.