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 2 ng. Peak blood levels as low as 130 ng/ml and as high as 3892 ng/ml were obtained in patients at 1-3 h following the oral administration of 0.6 mg/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 2 h after oral administration of the drug. Two hours after oral administration of 0.6 mg/kg of Oxsoralen, 8-MOP levels in the epidermis, dermis, and whole skin of the guinea pig (in ng/g) were: epidermis, 330 +/- 20; dermis, 89 +/- 16; whole skin, 379 +/- 19. Also detected were 8-MOP levels of 441 +/- 22 ng/ml in aqueous humor, 166 +/- 18 ng/ml in vitreous gel, 355 +/- 15 ng/g in lens, and 410 +/- 26 ng/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.