The development and evaluation of in vitro tests for photoirritancy

Photoirritancy, a reversible inflammatory reaction of the skin after chemical contact and UV radiation exposure, is increasingly observed as a side-effect of both cosmetics and certain systemic drugs. Despite the quantity of in vitro data available, none of the current animal models can be viewed as fully predictive of human exposure. It is therefore considered that the emphasis of future work should be the development and evaluation of in vitro assays. The aim of this study was to establish the interlaboratory performance of a physicochemical method, SOLATEX-PI. 12 pure chemicals at several concentrations were evaluated in the presence of UVA. In addition, a lymphoid cell assay was undertaken to allow a direct in vitro/in vitro comparison. The overall correlation between the laboratories was good when expressed in terms of a positive or negative result. However, there were some interlaboratory discrepancies, which were compounded by the lack of unequivocal in vivo data. Despite these discrepancies, both laboratories did agree on the final classification of nine of the 12 chemicals in the SOLATEX-PI system, based on the highest concentrations tested. The cellular photoirritancy assay, in contrast, predicted the correct classification for only eight of the 12 chemicals tested compared with the in vivo data supplied by IVI.