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To the Editor.—
The recent review of Dr Frank's textbook (Archives 116:234,1980) raised several questions about the stability of topical tretinoin in clinical use.The incompatibility of tretinoin with benzoyl peroxide or sunlight might be deduced from the following: marketed tretinoin products contain butylated hydroxytoluene, an antioxidant, to protect against the effects of atmospheric oxygen. Benzoyl peroxide labeling warns of its bleaching potential. Sunlight has similar properties. Mixing a highly unsaturated compound like tretinoin with very reactive oxidants such as benzoyl peroxide or ultraviolet radiation must necessarily destroy the tretinoin. Indeed, the J & J Pharmaceutical Research group could demonstrate that all tretinoin was lost within minutes after such exposures (data on file, Ortho Pharmaceuticals, Raritan, NJ).Furthermore, we can recall that the early benzoyl peroxide products themselves suffered from stability problems. Lotions had to be compounded at the time of dispensing to retain any