Idoxuridine

Idoxuridine is an antiviral medication used primarily to treat herpes simplex keratitis, a viral infection of the cornea of the eye. It is a synthetic pyrimidine nucleoside analog, specifically a thymidine analog, where the methyl group at the 5-position of thymidine is replaced by an iodine atom. This structural modification is key to its mechanism of action.

Once idoxuridine enters virus-infected cells, it is phosphorylated by viral thymidine kinase and then by cellular kinases to its active triphosphate form. This triphosphate form is then incorporated into viral DNA during replication. Because idoxuridine is structurally similar to thymidine, it is mistakenly recognized by viral DNA polymerase. However, the presence of the iodine atom disrupts normal DNA structure and function, leading to errors in replication and ultimately inhibiting viral DNA synthesis.

Idoxuridine is typically administered topically as an ophthalmic solution or ointment to the affected eye. It is most effective when treatment is initiated early in the course of the infection. While effective against herpes simplex virus, idoxuridine has a relatively narrow spectrum of activity and is not effective against other types of viruses. Due to potential toxicity and the availability of more effective and safer antiviral agents, its use has become less common in some regions, with drugs like acyclovir and ganciclovir often preferred for herpetic eye infections. Side effects can include local irritation, pain, and blurred vision.