Calculation of 8-methoxypsoralen dose according to body surface area in PUVA treatment

In 41 patients about to start PUVA, the dose of 8-methoxypsoralen (8-MOP) was calculated conventionally according to body weight (0.6 mg/kg), or according to body surface area (25 mg/m2) predicted from height and weight measurements. The two different methods of dosing were used on consecutive treatment days and the plasma 8-MOP concentration was measured on each occasion 2 h after ingestion of the crystalline form of 8-MOP, given to the nearest 10 mg. Body weight calculated doses ranged from 30 to 60 mg with a significant difference in the plasma 8-MOP concentration between the dose groups, indicating a systematic variation according to the weight of the patient. When calculated according to body surface area, only two doses were used (40 or 50 mg), and there was no significant difference in plasma 8-MOP concentration between the groups. Calculation of the dose of 8-MOP using body surface area may be performed quickly and simply provided the height and weight of individual patients is known. We provide evidence that this method of dosing will improve the therapeutic effect of PUVA in psoriasis.