Oral allylestrenol: A pregnancy-supporting progestogen

Abstract

Allylestrenol is a synthetic progestogen that has been in therapeutic use in the management of mild to severe cases of certain obstetric complications, like selected forms of miscarriage/abor-tion, threatened preterm labor, intrauterine growth restriction (IUGR), and gestational hypertension. Natural progesterone may be used for treatment; however, it has the property of being rapidly metabolized in the liver besides having little or no oral activity. While there are many other synthetic and orally adminis-trable progesterone analogs in the market, most of them, which are 19-nortestosterone derivatives, possess various undesirable side effects like symptoms of intolerance and a tendency to virilization. Allylestrenol, despite being a 19-nortestosterone derivative, has no known side effects including those attributed to the other members of its class, which is theorized to be due to subtle differences in its chemical structure, giving it a unique mechanism of action consisting of a triple effect—trophoblastic, placentotropic, and β2-adrenergic. The present review is mainly aimed at understanding the whys and wherefores behind the molecule’s moderate efficacy and remarkable safety along with examining the data from various studies.