Human models for identification of photosensitizing chemicals

The human is an appropriate and sensitive animal for identifying photosensitizing drugs administered either topically or systemically. Topically effective phototoxic agents are quite easily revealed when they are applied to normal or scarified skin which is subsequently exposed to 2 X 10(5) J.m-2 of near UV light (UVA, 320-400 nm). Systemically effective phototoxic drugs can be identified by exposing intradermally injected sites to either solar-simulating or UVA radiation. Drugs that cause photocontact allergy can usually be recognized by irradiating pretreated sites six times over a 3-week period with a solar simulator and then challenging the sites with UVA. Existing models, the human model especially, should make it possible to recognize important photosensitizing drugs before they are marketed.