Photocarcinogenicity of drugs

A number of commonly used medications including quinolone antibiotics, psor alens and various tetracycline derivatives are photosensitizers. These chem icals enhance the erythema response to sunlight. The effect of such exposur es on cancer risk has only been quantified in humans for oral psoralen phot ochemotherapy (PUVA). The experience of a cohort of 1380 patients followed for more than 20 years who received PUVA therapy for the treatment of psori asis documents that long-term high dose exposure to PUVA greatly increases the risk of squamous cell carcinoma. After 15 years, the risk of melanoma i s also increased among high dose patients. With PUVA therapy, an agent whic h is immunosuppressive in the skin, induces psoralen DNA adducts, is genoto xic and mutagenic. Substantially increased risk is only observed after many purposeful exposures to ultraviolet and this drug. These data suggest that at least some photosensitizing chemicals can substantially increase the ri sk of skin cancer in humans, but long-term multiple exposures appear to be necessary for a clinical meaningful increase of risk. (C) 1998 Elsevier Sci ence Ireland Ltd. All rights reserved.