#photostability

A retinoid exhibiting identical chromatographic and spectral characteristics of isotretinoin was observed in the samples from the skin exposed to light, but was virtually absent in the skin samples maintained in the dark. From single topical application of tretinoin, isotretinoin was as abundant as tretinoin in the chamber receiver solution, dermis, epidermis, and on the skin surface at 24 h after topical application. The data suggest the possibility that isotretinoin may have an important role in the pharmacology of topically applied tretinoin.

Tretinoin gel 0.025% has been shown to degrade under a variety of light conditions. In this study, tretinoin degradations of 85 to 90 percent were seen in fluorescent light and 84 to 89 percent in simulated solar light with tretinoin 0.025% formulated in a conventional gel vehicle.