PUVA therapy for psoriasis: Comparison of oral and bath-water delivery of 8-methoxypsoralen

A direct clinical comparison has been made of the efficacy of oral 8-methoxypsoralen with bath-water delivery of 8-methoxypsoralen during psoralen ultraviolet A (PUVA) phototherapy for a group of forty patients with stable plaque-type psoriasis vulgaris. The 8-methoxypsoralen concentration was 3.7 mg/liter in the bath water. The efficacy of these treatments was assessed by their ability to improve or clear the psoriasis. The skin of eight of the twenty patients with oral psoralen cleared, and another eight showed good improvement. Of the twenty patients who received 8-methoxypsoralen in bath water, eight patients had clearing of the skin, whereas nine patients had good improvement during the initial 8-week treatment period. Administration of 8-methoxypsoralen in bath water required much lower ultraviolet A irradiance to achieve maximum improvement. There were no systemic side effects in the patients treated by bath-water delivery; however, some patients did develop phototoxic erythema. Minimal phototoxic doses were also studied in patients and in volunteers using both routes of psoralen delivery. The minimal phototoxic dose threshold after psoralen bath delivery gradually declined over five treatments from 5.3 ± 0.6 joules/cm 2 to 2.8 ± 0.3 joules/cm 2, suggesting an accumulation of psoralen in the skin with this method of drug delivery. Bath-water delivery of 8-methoxypsoralen was therefore found to be as effective as oral administration of 8-methoxypsoralen and yet required smaller amounts of ultraviolet A radiation and yielded fewer side effects. It would thus seem to be confirmed as a useful alternative means of 8-methoxypsoralen administration in PUVA therapy.