Phototoxicity of New Psoralen-Containing Gels and Creams Versus Bath PUVA
Peerapat Nimkulrat, MD*, Vichit Leenutaphong, MD*, Srismorn Sudtim, BEd*
Affiliation : * Department of Dermatology, Siriraj Hospital, Mahidol University
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 prepa-
ration may be a good candidate for safe, convenient, and useful regimen in the topical PUVA therapy.
Objectives : 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.
Materials and 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 volun-
teers 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 narrow-
band 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).
Conclusion : The present study shows that the threshold of phototoxic response of 0.0025% 8-MOP gel indi-
cated 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 penetra-
tion 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.
Keywords : Bath PUVA, Psoralen–Containing gels, Psoralen–containing creams, Topical PUVA
