Tretinoin-- is the pharmaceutical form of retinoic acid. One of several retinoids, it is the carboxylic acid form of vitamin A and is also known as all-trans retinoic acid (ATRA). It is a first generation topical retinoid commonly used topically to treat acne vulgaris. It is also used orally to treat acute promyelocytic leukemia (APL). Its isomer, isotretinoin, is also an acne drug.