DRUG-INDUCED PHOTOSENSITIVITY

Characteristics and diagnosis of photosensitivity are discussed, and d rugs available in the United States that cause photosensitivity are id entified. In phototoxic reactions, the drug absorbs energy from ultrav iolet A (UVA) light and releases it into the skin, causing cellular da mage. In photoallergic reactions, light may cause a structural change in a drug so that it acts as a hapten, possibly by binding to proteins in the skin. Once a hapten-protein complex is formed, Langerhans' cel ls residing in the epidermis can present the antigen to immunocompeten t cells, causing hypersensitivity. Phototoxicity is much more common t han photoallergy. Drugs that can cause phototoxic reactions include am iodarone, quinolones, and tetracyclines. Drugs that have been associat ed with photoallergic reactions include thiazides and benzocaine. Phar macists should be aware of drugs that can cause photosensitivity and s hould counsel patients taking these drugs to avoid excessive exposure to sunlight.