Hydrocortisone caproate is a synthetic steroid hormone and 21-O-hexanoyl derivative of hydrocortisone. Hydroxyprogesterone caproate was previously marketed under the trade name Delalutin by Squibb, which was approved by the U.S. Food and Drug Administration (FDA) in 1956 and withdrawn from marketing in 1999. Hydrocortisone caproate acts by binding to progesterone receptors in the uterus, ovaries, breasts and in the central nervous system. These receptors exist in 2 isoforms, PR-A and PR-B. Hydrocortisone caproate binding to these receptors ultimately leads to regulation of gene transcription. This results in an anti-inflammatory effect which blunts the proinflammatory state that occurs with the initiation of labor and maintains uterine quiescence by stabilizing progesterone acting on the myometrium. Following intramuscular injection, approximately 50% of hydroxyprogesterone caproate metabolites are eliminated in the feces, while approximately 30% of metabolites are eliminated in the urine. Injection site pain is the most common adverse effect associated with hydroxyprogesterone caproate. Other commonly reported adverse effects include injection site swelling, urticaria, pruritus, injection site pruritus, nausea, injection site nodule, and diarrhea.