Plasma levels of 8-methoxypsoralen following PUVA-bath photochemotherapy

Administration of 8-methoxypsoralen (8-MOP) in a dilute bath water solution is an effective therapeutic alternative to oral PUVA therapy, avoiding systemic side effects, offering better bioavailability of the psoralen and requiring much smaller amounts of UVA for induction of therapeutic effects. To obtain exact data about the percutaneous absorption of 8-MOP during a psoralen bath, the plasma levels of the drug were determined in 26 patients with different skin diseases by a reverse high-performance liquid chromatographic method. Fifteen patients receiving oral PUVA therapy (0.8 mg 8-MOP/kg body weight) served as a positive control group. Bath solutions were prepared by diluting 15 ml of 0.5% stock solution of 8-MOP in 150 l of bath water (0.5 mg/l, 37°C). Blood samples were drawn from patients 5, 30, 60, 120 and 180 min after the bath. In the oral PUVA group, blood samples were obtained 1½ h after administration of the drug. In 23 of 26 patients, 8-MOP levels were undetectable in every blood sample. After 30 min, two patients showed detectable levels of 8-MOP (5 ng/ml, 7 ng/ml), while 60 min after the PUVA bath 8-MOP was detectable in only one volunteer (5 ng/ml). In patients receiving oral 8-MOP therapy, serum levels varied between 45 and 360 ng/ml 1½ h after drug administration. Our data confirm extremely low 8-MOP levels resulting from 8-MOP bath water treatments and provide confirmation of the absence of systemic side effects in patients who are undergoing PUVA-bath therapy.