[Influence of retinoids on the bioavailability of methoxy-8-psoralen]

The retinoid-PUVA combination has been recognized as a satisfactory treatment of psoriasis. The absorption of 8-methoxypsoralen (8-MOP) is subject to wide interindividual variations under the influence of factors that are not yet known with certainty but are independent of age, sex and food taken at the same time as the psoralen. Whether concomitant retinoid administration influences the bioavailability of 8-MOP was considered an interesting question. The pharmacokinetics of 8-MOP were studied and compared in two populations of psoriatic patients: 119 patients treated with PUVA alone (psoralen-ultraviolet A) and 40 patients treated with the etretinate-PUVA combination (RePUVA). 8-MOP was assayed by the modified Ljunggren method 1 h, 1 h 30, 2 h, 2 h 30, 3 h and 4 h after ingestion of 8-MOP. The pharmacokinetic values recorded were: time and peak value of maximum plasma 8-MOP concentration (Tmax, Cmax) and area under the curve of time-related 8-MOP concentrations (AUC). The results obtained were as follows: Tmax PUVA 2 h 02 +/- 53 min RePUVA 1 h 56 +/- 50 min Cmax PUVA 159.12 +/- 88.85 ng/ml RePUVA 163.63 +/- 92.85 ng/ml AUC PUVA 343.33 +/- 211.06 ng*h/ml RePUVA 388.12 +/- 251.03 ng*h/ml Statistical analysis showed no significant difference in pharmacokinetic values between patients on PUVA alone and patients on RePUVA. Taking etretinate therefore does not alter the pharmacokinetics of 8-MOP and should not require any change in PUVA treatment.