Photochemotherapy of Psoriasis with Oral Methoxsalen and Longwave Ultraviolet Light

Oral administration of a photoactive drug, 8-methoxypsoralen (methoxsalen), followed by exposure to a high-intensity, longwave ultraviolet-light system resulted in complete clearing of generalized psoriasis in 21 patients. In 16 of these cases, a paired comparison showed methoxsalen followed by longwave ultraviolet light to be more effective than conventional ultraviolet light. 8-Methoxypsoralen followed by exposure to longwave ultraviolet light has previously been shown to inhibit epidermal DNA synthesis; this may be its mechanism of action in psoriasis, a disorder characterized by an accelerated cell cycle and rate of DNA synthesis. The term photochemotherapy is used to emphasize the point that the effect on epidermal proliferation and the therapeutic response require the interaction of light and drug. (N Engl J Med 291:1207–1211, 1974)