8-Methoxypsoralen Levels in Blood of Vitiligo Patients and in Skin, Ophthalmic Fluids, and Ocular Tissues of the Guinea Pig

8-Methoxypsoralen (8-MOP) levels in the blood of vitiligo patients were determined through the use of a reverse- phase high-performance liquid chromatographic method. The overall recovery of the internal standards was 85-94%, with the lower detection limit of 8-MOP at 2ng. Peak blood levels as low as 130ng/ml and as high as 3892 ng/ml were obtained in patients at 1-3h following the oral administration of 0.6mg/kg body weight of Oxsoralen capsules (Elder Pharmaceuticals Co.). These results are consistent with the clinical observation that maximum response in phototherapy is obtained at about 2h after oral administration of the drug. Two hours after oral administration of 0.6mg/kg of Oxsoralen, 8-MOP levels in the epidermis, dermis, and whole skin of the guinea pig (inng/g) were: epidermis, 330 ± 20; dermis, 89 ± 16; whole skin, 379 ± 19. Also detected were 8-MOP levels of 441 ± 22ng/ml in aqueous humor, 166 ± 18ng/ml in vitreous gel, 355 ± 15ng/g in lens, and 410 ± 26ng/g in retina. These results point to the fact that the eyes of the patient must be protected from exposure to sunlight after psoralen UV treatment, and that 8-MOP is absorbed in blood unevenly and varies from patient to patient. The fact that only 50-60% of the patients responded to psoralen photochemotherapy for vitiligo may be related to the variation of absorption of the drug in individual patients.