[Differentiation of the antipsoriatic and phototoxic effectiveness of topical PUVA therapy].

Using a 0.075% 8-methoxypsoralen solution, minimal phototoxic doses and improvement of psoriasis lesions were investigated in 15 patients suffering from chronic stationary psoriasis. The time interval between topical 8-methoxypsoralen application and long-wave ultraviolet light irradiation was increased stepwise. The mean minimal phototoxic dose declined with increasing time interval and reached its minimum 2 h after 8-methoxypsoralen application. In spite of that, antipsoriatic efficiency was maximal 15 min after application. In order to obtain a favorable relationship between antipsoriatic efficiency and unwanted side effects when using topical PUVA treatment, irradiation should be started 15 min after 8-methoxypsoralen application.