Photochemotherapy of psoriasis with relevance to 8-methoxypsoralen plasma level and low intensity irradiation.

The 8-methoxypsoralen (8-MOP) plasma level was determined in 31 patients during treatment with PUVA (psoralen + UVA light). The UVA light source was of a low intensity type, giving only 2 mW/sec/cm2 and required an irradiation time of 30 minutes. The lesions of 19 patients healed completely. Following an oral dose regimen adjusted to the patient's weight, the 8-MOP values at 2 hours varied from 2 ng/ml to 167 ng/ml (mean 56 ng/ml). There was no clearcut relation between the 8-MOP plasma level and the clinical response but in 9 patients there was a prompt response to treatment when the dose of psoralen was increased by 10 mg. In 5 patients the 8-MOP plasma levels was determined hourly for the first 4 hours and showed a peak at 2 hours except in one patient with very low values who had a peak at 4 hours. The augmentation of pigmentation was measured by means of reflectometry on three univolved areas. Two peaks were observed--one during the first week and the other after 2--3 weeks of therapy.