Phototoxicity of new psoralen-containing gels and creams versus bath PUVA.

BACKGROUND

Bath-PUVA-photochemotherapy has become a useful alternative to oral PUVA therapy due to a number of advantages over systemic PUVA, for example, no ophthalmologic risk and nausea, and a lower cumulative UVA doses. However, its major disadvantage is the logistical requirement for bath tubs in practice and some patients feel uncomfortable to share the same bath with others. Topical psoralen contained preparation may be a good candidate for safe, convenient, and useful regimen in the topical PUVA therapy.

OBJECTIVE

The purpose of the present study was to investigate the intensity of the phototoxic response of 8-MOP bath solution to different concentrations of preparations of 8-MOP gels and creams.

METHODS

Following informed consent, the test bath solution (0.375%), gels (0.0025% to 0.010%) and creams (0.0025% to 0.010%) were applied to the normal-appearing skin of the upper back of 23 volunteers who had no history of photosensitivity. The escalating UVA doses (0.25 to 7.0 J/cm2) were given 15 minutes after application of test substances. Seventy-two hours after UVA exposure minimal phototoxic doses (MPD) were defined visually and the intensity of the erythema response was also assessed by using a narrowband spectrophotometer The MPD and the dose-response curves for erythema response of the gels and creams were compared with those of the bath.

RESULTS

There were no significant differences between the overall mean MPD of tested gels and that of bath solution (p > 0.05). On the contrary, the cream preparations induced phototoxic response (MPDs) to a lesser degree than bath solution and gels (p < 0.05). When comparing the slope of the dose-response curve for erythema of 0.0025% and 0.0100% gel to that of the bath solution, the correlation is very strong (R2 = 0.987 and 0.936, respectively, p < 0.0001).

CONCLUSIONS

The present study shows that the threshold of phototoxic response of 0.0025% 8-MOP gel indicated by MPD is well correlated with those of the bath solution. The slope of the dose-response curve for erythema of this preparation also significantly corresponded to that of the bath solution. Thus, the penetration and drug delivery of 0.0025% 8-methoxypsoralen gel may be similar to 8-methoxypsoralen bath solution. This preparation may be a good candidate for a useful therapeutic modality for topical PUVA therapy, and further clinical trial should be performed.