The influence of food on 8-methoxypsoralen serum concentration and minimal phototoxic dose

Ten adult volunteers were given three oral doses of 0.46-0.56 mg/kg body weight of 8-methoxypsoralen (8-MOP) in a liquid formulation under fasting conditions, and after ingestion of a low-fat or fat-rich breakfast. 8-MOP serum levels and photosensitivity were measured 0.5-4 h after drug ingestion. The 1-h 8-MOP serum levels and photosensitivity were significantly higher in fasting conditions than after ingestion of a low-fat or fat-rich meal (intra-individual median difference in photosensitivity 7.5 J/cm2). On 12 of 20 occasions when the drug was taken after food ingestion, the 1-h 8-MOP serum concentration was below 30 ng/ml. A survey of 43 out-patients undergoing regular PUVA treatment showed that the frequency of erythemal reactions was significantly higher when 8-MOP was ingested with a > 50% smaller quantity of food than usual (P < 0.005). This study demonstrated food-induced variations in 8-MOP photosensitivity both in an experimental situation and in an out-patient survey. In order to optimize the therapeutic effect of PUVA, the quantity of food taken before 8-MOP should remain constant, and the timing of UVA irradiation should be adjusted according to the preceding food intake.