Idoxuridine (Herplex) is a water-soluble iodinated deriv-ative of deoxyuridine that inhibits several DNA viruses including HSV, VZV, vaccinia, and polyoma virus. The triphosphorylated metabolite of idoxuridine inhibits both viral and cellular DNA synthesis and is also incor-porated into DNA. Such modified DNA is susceptible to strand breakage and causes aberrant viral protein syn-thesis. Because of its significant host cytotoxicity, idoxuri-dine cannot be used to treat systemic viral infections. The development of resistance to this drug is common.
Idoxuridine is marketed strictly for topical ophthalmic use, and systemic exposure is insignificant. However, af-ter oral dosing, the drug is rapidly metabolized and ex-creted. It tends not to accumulate in body tissues.
The only FDA-approved use of idoxuridine is in the treatment of herpes simplex infections of the eyelid, con- junctiva, and cornea. It is most effective against surface infections because it has little ability to penetrate the tis-sues of the eye. intravenous idoxuridine was designated an orphan drug for the treatment of soft tissue sarcoma.
Idoxuridine may cause local irritation, mild edema, itch-ing, and photophobia. Corneal clouding and small punc-tate defects in the corneal epithelium have been re-ported. Allergic reactions are rare.