5-Methoxypsoralen, a naturally occurring linear
furocoumarin, has been successfully used in combination with ultraviolet (UV) A irradiation [
psoralen plus UV (PUVA)] to manage
psoriasis and
vitiligo. In patients and volunteers, PUVA
5-methoxypsoralen causes a dose-related increase in cutaneous photosensitivity. However, mean minimum phototoxic doses (MPD) were 30 to 50% greater with
5-methoxypsoralen than with
8-methoxypsoralen within individuals; this suggests lower photoactivity with
5-methoxypsoralen. In comparative clinical trials of parallel design,
psoriasis clearance rates of > 90% or > 97% were observed in similar numbers of patients (60 to 77%) receiving oral PUVA
5-methoxypsoralen (typically 1.2 mg/kg) or oral PUVA
8-methoxypsoralen (0.6 mg/kg) treatment. Generally,
5-methoxypsoralen recipients required a greater total UVA exposure than
8-methoxypsoralen recipients to achieve end-point. However, study end-point was achieved sooner with oral or topical PUVA
5-methoxypsoralen in a small number of patients with
psoriasis who received both treatments simultaneously and contralaterally. Up to 56% of patients with
vitiligo achieved > 75% repigmentation with
5-methoxypsoralen (oral or topical) combined with UV irradiation (lamp or sun); the face and trunk were the most responsive areas. Lack of response to PUVA
5-methoxypsoralen treatment was observed in up to 16% of patients with
psoriasis and, in 1 trial, in 22% of those with
vitiligo. Lesion spreading during treatment of
vitiligo was also observed in 7 (19%) patients in 1 study. The incidence and severity of adverse events was generally lower in PUVA
5-methoxypsoralen 1.2 mg/kg than in PUVA
8-methoxypsoralen 0.6 mg/kg recipients.
Nausea and/or
vomiting,
pruritus and
erythema were the most commonly reported adverse events in the short term; they occurred about 2 to 11 times more frequently in
8-methoxypsoralen than
5-methoxypsoralen recipients within clinical trials. Adverse hepatic events after
oral administration of the
drug were uncommon. Long term tolerability data for PUVA
5-methoxypsoralen are scarce; however, carcinogenicity was not reported during a 14-year observation period of 413 patients with
psoriasis.
CONCLUSION: