Topical tretinoin or adapalene in acne vulgaris: an overview

Retinoids target several pathoetiologic events of acne vulgaris. The undisputed efficacy of tretinoin, and yet its underutilization, due to apprehension of retinoid dermatitis, triggered a search for newer, well-tolerated retinoids. The discovery of nuclear retinoic acid receptors has provided clues to a rational design of synthetic, receptor-selective retinoic acid agonists. Adapalene is an addition to the arsenal of topical retinoids. It possesses the biological properties of tretinoin, but has a distinct physiochemical profile, including high lipophilicity and increased chemical and photostability. It exhibits selective affinity for nuclear retinoic acid receptors and does not bind to cytosolic retinoic acid binding proteins. It exemplifies the formulation of a novel retinoid with specific pharmacologic profile and clinical objectives. Accordingly, numerous clinical trials have compared adapalene and tretinoin in the management of acne vulgaris and concluded that tretinoin 0.05% gel exhibits a greater anti-acne efficacy than adapalene 0.1% gel, but has higher skin irritation potential. This article reviews the pharmacology of adapalene, including its retinoid receptor binding profile, antiproliferative effects, cell differentiation modulation, comedolytic and anti-inflammatory activity, and specifically focuses on the comparison of the efficacy and irritation profile of adapalene and tretinoin.