Investigation on the photostability of a tretinoin lotion and stabilization with additives.

Tretinoin, a drug that is used in topical preparations for the treatment of acne vulgaris, is known to be very susceptible to degradation under daylight. The objective of this work was to investigate the degradation of a tretinoin lotion placed in front of a xenon lamp. Analysis was performed with HPLC. The tretinoin lotion was degraded to about 20% of its initial concentration within 30 min. Incorporation of tretinoin in beta-cyclodextrin or in some surfactants (Brij(R)s) did not have any effect on the photodegradation of tretinoin. Neither could a UV-B sunscreen retard the photodegradation of tretinoin while a UV-A sunscreen had very little effect. Irradiation with selected wavelengths revealed that 420 nm seemed to be the most harmful wavelength for the degradation of tretinoin and not the wavelength of maximum absorption (350 nm) as expected. Then the addition of the yellow colourants chrysoin and fast yellow, absorbing in the region of 420 nm, was tested. These colourants did indeed retard the photo-degradation of tretinoin more or less depending on the concentration of the dye. Finally we only had to select a concentration that was still effective but that did not colour the skin.