Hydroxyprogesterone caproate (OHPC), sold under the brand names Proluton and Makena among others, is a progestin medication which is used to prevent preterm birth in pregnant women with a history of the condition and to treat gynecological disorders. It has also been formulated in combination with estrogens for various indications (brand names Gravibinon and Primosiston) and as a form of long-lasting injectable birth control (brand name Chinese Injectable No. 1). It is not used by mouth and is instead given by injection into muscle or fat, typically once per week to once per month depending on the indication.OHPC is generally well tolerated and produces few side effects. Injection site reactions such as pain and swelling are the most common side effect of OHPC. The medication may increase the risk of gestational diabetes when used in pregnant women. OHPC is a progestin, or a synthetic progestogen, and hence is an agonist of the progesterone receptor, the biological target of progestogens like progesterone. It has some antimineralocorticoid activity and no other important hormonal activity. The medication shows a number of differences from natural progesterone.OHPC was discovered in 1953 and was introduced for medical use in 1954 or 1955. It was marketed in the United States under the brand name Delalutin and throughout Europe under the brand name Proluton. The medication was discontinued in the United States in 1999. However, OHPC was subsequently reintroduced in the United States under the brand name Makena for the treatment of preterm birth in 2011.
However, there was a higher incidence of injection site pain with subcutaneous autoinjection than with intramuscular injection (37.3% vs. 8.2%). Distribution
OHPC is extensively bound to plasma proteins, of which include albumin. Unlike progesterone and 17α-hydroxyprogesterone, OHPC has very low affinity for corticosteroid-binding globulin (less than 0.01% of that of cortisol). Progesterone and 17α-hydroxyprogesterone have low affinity for sex hormone-binding globulin, and for this reason, only a very small fraction of them (less than 0.5%) is bound to this protein in the circulation. Metabolism
OHPC appears to be metabolized primarily by the cytochrome P450 enzymes CYP3A4 and CYP3A5. It may also be metabolized by CYP3A7 in fetal liver and the placenta. Unlike progesterone, OHPC is not metabolized by traditional steroid-transforming enzymes and does not form similar metabolites. The metabolism of OHPC is by reduction, hydroxylation, and conjugation, including glucuronidation, sulfation, and acetylation. The caproate ester of OHPC is not cleaved during metabolism, so 17α-hydroxyprogesterone is not formed from OHPC. As such, OHPC is not a prodrug of 17α-hydroxyprogesterone, nor of progesterone.OHPC has been found to have an elimination half-life of 7.8 days when given by intramuscular injection in an oil-based formulation to non-pregnant women. Its total duration is said to be 10 to 14 days, which is much longer than the duration of intramuscularly administered progesterone in an oil formulation (2 to 3 days). In pregnant women, the elimination half-life of OHPC appears to be longer, about 16 or 17 days.