Further studies on allopurinol therapy and human cataractogenesis.

We examined 11 cataractous lenses (or aspirated lens matter from extracapsular extractions) from patients ranging in age from 55 to 84 years who used allopurinol on a long-term basis (more than two years). Phosphorescence analyses demonstrated the characteristic allopurinol triplet in these lenses. When we analyzed normal lenses from patients taking allopurinol in a similar manner we found no evidence of allopurinol photobinding. These data indicated that allopurinol has a cataractogenic action only in patients in whom the drug has become photobound within the lens. Long-term allopurinol therapy does not necessarily cause or enhance cataracts in all patients. There may be a relationship between ultraviolet radiation exposure and circulating allopurinol levels (and perhaps renal function) in the genesis of photosensitized allopurinol cataracts.