KINETICS OF PHOTOSENSITIVITY IN BATH-PUVA PHOTOCHEMOTHERAPY

Background: Bath-PUVA is used to treat a variety of dermatoses. Howeve r, the kinetics of 8-methoxypsoralen during treatment are not complete ly clarified. Objective: The purpose of this study was to investigate the intensity of the phototoxic response and the persistence of photot oxicity after bath-PUVA. Methods: Twelve volunteers were exposed to WA doses ranging from 0.5 to 40 J/cm(2) from 10 to 240 minutes after bat h-PUVA treatment. The resulting phototoxic response of the skin was de termined. Results: Irradiation 10 minutes after the psoralen bath led to the lowest assessed minimal phototoxic dose (MPD) of 1.42 J/cm(2) ( mean, SD +/- 0.29). Thereafter, the MPD increased significantly and sh arply every hour. At 4 hours after the psoralen bath, UVA doses up to 40 J/cm(2) failed to induce any phototoxic erythema (MPD). Conclusion: For optimal effects, UVA irradiation has to be administered immediate ly after the psoralen bath; no restrictive behavior is necessary after bath-PUVA treatment.