After oral intake, 5-methoxypsoralen (5-MOP) is as effective as 8-MOP for PUVA therapy for psoriasis, with a lower incidence of acute cutaneous side effects.

We compared bath-water delivery of 5-MOP and 8-MOP for photochemotherapy of psoriasis.

Twenty-two patients underwent phototesting with 0.0003% 5-MOP or 8-MOP aqueous solutions. Twelve patients with palmar psoriasis were studied with a side-to-side comparison, and 10 patients with recurrent plaque-type psoriasis were treated with one therapy or the other.

Minimal phototoxic dose (MPD) values were 2.8 ± 1.2 J/cm² with 8-MOP and 2 2.0 ± 1.2 J/cm2 with 5-MOP (p < 0.01). Both therapies cleared palmar lesions but 8-MOP required more UVA irradiation (46.3 ± 21.0 J/cm2 vs 30.2 ± 21.5 J/cm2; p < 0.01) and more exposures (21.0 ± 6.0 vs 17.0 ± 5.0; p = 0.02). Bath-5-MOP-UVA was also more effective in the treatment of plaque-type psoriasis (cumulative UVA doses, 56.8 ± 39.2 vs 59.1 ± 27.9 J/cm2; number of exposures, 20.0 ± 5.7 vs 21.6 ± 4.7), but these differences were not significant (p = NS). Patients developed an intense tan significantly earlier with 5-MOP than with 8-MOP (3.5 ± 0.5 weeks vs 4.4 ± 0.5 weeks; p < 0.01).

Bath-5-MOP-UVA was more phototoxic than bath-8-MOP-UVA. It was more effective in the treatment of palmar psoriasis, whereas its greater pigmentogenic activity appeared to have an adverse effect on therapeutic effectiveness in the treatment of plaque-type psoriasis.