Variations in skin photosensitization during repeated oral 8-methoxypsoralen medication

Nine adult volunteer dermatological patients were subjected to five repeated oral exposures of 0.6 mg/kg of 8-methoxypsoralen at near-fasting conditions. In the individual volunteer, the plasma 2-h drug level varied by a factor of 1.3 to 7.1, mean 3.5. The simultaneously measured skin minimal UVA sensitivity varied in the individual subjects by a factor of 1.3 to 3.8, mean 2.2. When all serum level and skin photosensitivity data of the study were tabulated, a negative correlation factor of 0.5758 was obtained, which is statistically highly significant (P less than 0.001). It is concluded that both serum drug levels and degree of skin photosensitivity may fluctuate considerably in a single subject during repeated exposures to a standard oral 8-methoxsalen dose. Attempts should be made to minimize such undesirable variation by improvements of drug formulations and better consideration of the influence of dietary factors on drug absorption.