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 daylig ht. The objective of this work was to investigate the degradation of a tret inoin lotion placed in front of a xenon lamp. Analysis was performed with H PLC. The tretinoin lotion was degraded to about 20% of its initial concentr ation 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 o f tretinoin while a UV-A sunscreen had very little effect. Irradiation with selected wavelengths revealed that 420 nm seemed to be the most harmful wa velength for the degradation of tretinoin and not the wavelength of maximum absorption (350 nm) as expected. Then the addition of the yellow colourant s 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 s elect a concentration that was Still effective but that did not colour the skin. (C) 2000 Elsevier Science B.V. All rights reserved.