OHPC has been studied in humans at doses as high as 5,000 mg per week by intramuscular injection, with safety and without glucocorticoid effects observed. The medication does interact with the glucocorticoid receptor however; it has about 4% of the affinity of dexamethasone for the rabbit glucocorticoid receptor. But it acts as a partial agonist of the receptor and has no greater efficacy than progesterone in activating the receptor and eliciting associated gene expression in vitro. Other activities
As a pure progestogen, OHPC has no androgenic, antiandrogenic, estrogenic, or glucocorticoid activity. The absence of androgenic and antiandrogenic activity with OHPC is in contrast to most other 17α-hydroxyprogesterone-derivative progestins. Due to its lack of androgenic properties, similarly to progesterone, OHPC does not have any teratogenic effects on the fetus, making it safe for use during pregnancy. Although OHPC has been described as a pure progestogen, there is evidence that it possesses some antimineralocorticoid activity, similarly to progesterone and 17α-hydroxyprogesterone. This includes clinically important diuretic effects and reversal of estrogen-induced fluid retention and edema. Unlike progesterone, OHPC and its metabolites are not anticipated to interact with non-genomic receptors such as membrane progesterone receptors or the GABAA receptor. In accordance, OHPC is not thought to possess the neurosteroid activities of progesterone or its associated sedative effects.In relation to cytochrome P450 enzymes, OHPC has no effect on CYP1A, CYP2D6, CYP2C9, or CYP3A4, but is a modest inducer of CYP2C19. Differences from progesterone
There are pharmacodynamic differences between progesterone and OHPC, which may have implications for obstetrical use.
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.