Lack of photosensitization of ocular tissues by allopurinol.

Based on careful double-blind studies using albino mouse ocular tissues, we conclude that allopurinol does not act as a photosensitizer for ocular tissue damage in mice relative to exposure to environmental near ultraviolet (UV) light. Damage to lens epithelial cells and retinal photoreceptors was equivalent in UV light-exposed mice that were either fed or not fed a dose of allopurinol equivalent to that used by humans in the treatment of gout. There was also no direct in vitro photosensitizing interaction between allopurinol and protein or nucleic acids. We conclude that patients in whom cataracts developed after using allopurinol and exposure to high irradiances of near UV light were most likely affected by the UV light itself.