AVITA® Gel, a topical retinoid, contains tretinoin 0.025% by weight in a gel vehicle of butylated hydroxytoluene, hydroxypropyl cellulose, polyolprepolymer-2, and ethanol (denatured with tert-butyl alcohol and brucine sulfate) 83% w/w. Chemically, tretinoin is all-trans-retinoic acid (C₂₀H₂₈0₂; molecular weight 300.44 vitamin A acid) and has the following structural formula: