Chemical stability of adapalene and tretinoin when combined with benzoyl peroxide in presence and in absence of visible light and ultraviolet radiation.

Adapalene and tretinoin are molecules used in the topical treatment of acne vulgaris. Commercial formulations (adapalene 0.1% gel and tretinoin 0.025% gel) were mixed with equal volumes of commercially available benzoyl peroxide formulation (10% lotion) and subsequently exposed to light over 24 h. With and without exposition to light, adapalene exhibits a remarkable stability whereas tretinoin is very sensitive to light and oxidation. The combination of benzoyl peroxide and light results in more than 50% degradation of tretinoin in about 2 h and 95% in 24 h.