Acitretin is a retinoid analog of vitamin A and active metabolite of another developmental toxicant, etretinate, which it is gradually replacing in the marketplace. It has therapeutic activity in treating severe psoriasis and other skin (keratinizing) disorders. Its mechanism of action is that of etretinate, by bonding to specific nuclear receptors and modulating gene expression. Acitretin is available as a prescription drug under the trade names Neotigason® or Soriatane®, and it has a pregnancy category of X. In laboratory animals, acitretin is a potent teratogen by the oral route, producing malformations in rabbits, mice, and rats in decreasing order of sensitivity related to dosage. In the human, acitretin has, as stated in the package insert, been associated with birth defects in the progeny of women treated during pregnancy. Acitretin is the hydrolyzed derivative of etretinate. It is a large molecule of high hydrophobicity that can participate in donor/acceptor hydrogen bonding.