Current status of predictive animal models for drug photoallergy and their correlation with drug photoallergy in humans.

The number of adverse responses considered to be drug photosensitivity reactions account for only an exceedingly small percentage of the total undesirable effects from environmental chemicals. However, the rising incidence of and severe disability resulting from drug photosensitivity, especially when the photosensitivity is of the persistent light reactor type, indicate that increased photobiologic research and development efforts are required. Predictive tests are an obvious approach to minimize or eliminate those chemicals showing a risk-benefit ratio that is undesirable to society in general or to an unknowing individual in particular. Animal models with predictive value for determining the risk of photoallergic contact dermatitis in humans have undergone considerable modification during the past decade. This study reports an improved experimental guinea pig model for inducing photoallergic contact dermatitis to musk ambrette. In contrast to previously described models that used Freund's adjuvant, this model does not require nuchal stripping with cellophane tape. Control studies for primary irritancy, phototoxicity, allergic contact dermatitis, and "angry back" syndrome were included in the experimental design. Only photoallergic contact dermatitis was observed. Although the technique used to demonstrate this phenomenon is conducive to standardization, additional studies are required to ascertain whether or not other chemicals known to be photoallergic in humans can also be demonstrated with this animal model.