Randomized, double-blind comparison of 1 mg/L versus 5 mg/L methoxsalen bath-PUVA therapy for chronic plaque-type psoriasis.

Background: Bath-psoralen plus ultraviolet A (PUVA) radiation therapy is increasingly replacing oral PUVA because of its superior short- and long-term safety profile. Several investigations in recent years have led to a refinement of the bath-PUVA protocol; however, the optimal therapeutic concentration of methoxsalen in the bath water has as yet not been delineated.

Objectives: The therapeutic efficacy and tolerability of bath-PUVA by using two different dilutions of methoxsalen (1 mg/L vs 5 mg/L or 0.0001% vs 0.0005%) were compared in 46 patients with chronic plaque-type psoriasis in a prospective, randomized, double-blind study.

Methods: Scores of the Psoriasis Area and Severity Index excluding psoriasis of the head (PASI(TUL)) and the Plaque Severity Index (PSI) were assessed at baseline and at biweekly intervals thereafter until (near)complete clearance or maximal improvement. In addition, methoxsalen plasma levels were determined immediately after the psoralen bath during the first week of treatment and treatment-related side effects were recorded throughout the entire study period.

Results: The median baseline PASI(TUL) score decreased from 11.7 (7.5-32.8) to 3.3 (0.6-1.2) (-72%) in the 1 mg/L methoxsalen group and from 10.8 (6.6-20.7) to 1.4 (03.2) (-87%) in the 5 mg/L methoxsalen group (P < .01). The median baseline PSI score decreased from 9 (6-12) to 3.1 (0.6-10) (-66%) in the 1 mg/L methoxsalen group and from 9.3 (7.3-12) to 1.6 (0-3.6) (-83%) in the 5 mg/L methoxsalen group (P < .01). The median cumulative UVA exposure dose was 25.4 (5.3-81.5) J/cm2 for 5 mg/L methoxsalen and 71.9 (20.7-587.3) J/cm2 for 1 mg/L methoxsalen (P = .001). The number of exposures (22 [11-29] vs 23 [11-34]) and treatment duration (43 [19-68] vs 44 [23-66] days) was comparable for both methoxsalen dilutions (P = .97). Median psoralen plasma levels were 0 (0-26) ng/mL after the 1 mg/L and 30 (0-64) ng/mL after the 5 mg/L methoxsalen immersion (P = .001). Mild to moderate adverse events were more common in the 5 mg/L methoxsalen group.

Limitations: The conclusions of this randomized controlled study are limited by the relatively small sample size.

Conclusions: Our data indicate that in bath-PUVA treatment the use of a high (5 mg/L) methoxsalen concentration is substantially more effective in clearing chronic plaque-type psoriasis than a low (1 mg/L) concentration.