Food-induced increase in bioavailability of 5-methoxypsoralen

5-Methoxypsoralen (5-MOP) in combination with ultraviolet light exposure is used for the treatment of psoriasis. The effect of food on the pharmacokinetics of 5-MOP was evaluated in a randomized, crossover study in nine healthy subjects. Each subject received the tablets with a standardized breakfast or under fasting conditions. The food had a dramatic effect on the bioavailability of 5-MOP. Five of the subjects showed no measurable quantities (detection limit of the analytical technique 1 ng.ml-1) of 5-MOP when the drug was given under fasting conditions. However, plasma peak concentration within the range 37-144 ng.ml-1 (median 102 ng.ml-1) was measured when the drug was taken with food. The time for the plasma peak concentration was within the range 2.0-5.1 h (median 3.0 h) under non-fasting conditions. The elimination half-life was within the range 1.4-2.7 h (median 1.9 h). We conclude that it is imperative that 5-MOP tablets are administered together with food.