Comparison of bioavailability and phototoxicity of two oral preparations of 5-methoxypsoralen.

5-Methoxypsoralen (5-MOP) (Psoraderm 5) tablets obtained from France and 5-MOP micronized in capsules (manufactured in our pharmacy department) were administered to seven psoriasis patients in a 1.2 mg/kg body weight dose schedule. Bioavailability and phototoxicity were compared. It was found that the maximum serum concentration and the area under the concentration curve were significantly higher (P less than 0.01) after administration of the capsules, indicating higher bioavailability. No erythema developed in any of the patients after administration of the tablets, whereas with the capsules four of the patients developed erythema at the test site. The absence of erythema following the use of the tablets is probably due to the poor bioavailability of this preparation.