Rapid Decline in Photosensitivity After 8-Methoxypsoralen Bathwater Delivery

In oral psoralen with UV-A (PUVA) photochemotherapy, bathwater delivery of psoralens is an attractive alternative to oral intake, since substantially lower cumulative UV-A doses are required for the completion of therapy and there are virtually no systemic side effects.1,2Little is known about theoptimal time point of UV-A irradiation following bathwater application of psoralens. Typically, patients are exposed to UV-A irradiation immediately after soaking in a psoralen bath, which, for instance, contains 8-methoxypsoralen (8-MOP), 0.5 to 1.0 mg/L. We have investigated how time affects photosensitivity following bathwater application of 8-MOP. Patients (Whites of skin type II-III), in whom PUVA bath therapy was chosen and initiated for the treatment of a variety of skin diseases, were bathed in warm water containing 8-MOP, 0.5 mg/L, for 20 minutes and the minimal phototoxic dose (MPD) was determined. Each patient (N = 25) was exposed to UV-A immediately after the 8-MOP bath and