Difference in bioavailability between two brands of 8-methoxypsoralen and its impact on the clinical response in psoriatic patients.

1 Several 8-methoxypsoralen (8-MOP) preparations are now available for photochemotherapy of psoriasis. To assess differences in clinical response two preparations marketed in The Netherlands, Oxsoralen capsules (Elder) and Meladinine tablets (Basotherm), were given to eight psoriatic patients. Serum concentrations and the minimal phototoxic dose (MPD) as a measure for clinical response were determined. 2 Bioavailability and serum peak concentrations were significantly higher for Maladinine in all patients and the MPD value favoured Maladinine in 5 of the 8 patients. The mean time of the serum peak concentrations was 1 h earlier for Maladinine than for Oxsoralen. 3 These findings are relevant not only for the choice of drug in individual patients but also for comparison of the results of multicentre trials performed in different parts of the world.