In another study that used an unspecified dosage of intramuscular OHPC, testosterone secretion was assessed in a single man and was found to decrease from 4.2 mg/day to 2.0 mg/day (or by approximately 52%) by 6 weeks of treatment, whereas secretion of luteinizing hormone remained unchanged in the man. Yet another study found that 3,000 mg/week OHPC by intramuscular injection suppressed testosterone levels from 640 ng/dL to 320–370 ng/dL (by 42–50%) in a single man with prostate cancer, which was similar to the testosterone suppression with cyproterone acetate or chlormadinone acetate. Gestonorone caproate, a closely related progestin to OHPC with about 5- to 10-fold greater potency in humans, was found to suppress testosterone levels by 75% at a dosage of 400 mg/week in men with prostate cancer. For comparison, orchiectomy decreased testosterone levels by 91%. In general, progestins are able to maximally suppress testosterone levels by about 70 to 80%. The antigonadotropic effects of OHPC and hence its testosterone suppression are the basis of the use of OHPC in the treatment of benign prostatic hyperplasia and prostate cancer in men. Suppression of luteinizing hormone levels by OHPC has also been observed in women. Glucocorticoid activity
OHPC is said not to have any glucocorticoid activity. In accordance, OHPC has been found not to alter cortisol levels in humans even with very high doses by intramuscular injection. This is of relevance because medications with significant glucocorticoid activity suppress cortisol levels due to increased negative feedback on the hypothalamic–pituitary–adrenal axis.
In contrast to progesterone, OHPC is not metabolized by traditional steroid-transforming enzymes and instead is metabolized exclusively via oxidation at the caproate side chain by cytochrome P450 enzymes. As such, it is not thought to have the same tissue-specific activation and inactivation patterns that progesterone does nor the same non-genomic actions that progesterone and its metabolites possess.Further clinical research is anticipated to provide additional data to help clarify the issue of safety with OHPC. In any case, it has been recommended by the American College of Obstetricians and Gynecologists that pregnant women treated with OHPC receive counseling about its risks and benefits. Pharmacokinetics
Absorption
In animals, the bioavailability of OHPC with intramuscular injection is nearly 100%, but its oral bioavailability is very low at less than 3%. In women, 70 mg/day oral OHPC has similar endometrial potency as 70 mg/day oral OHPA and 2.5 mg/day oral medroxyprogesterone acetate, indicating that oral OHPC and OHPA have almost 30-fold lower potency than medroxyprogesterone acetate via oral administration. Studies on progestogenic endometrial changes with oral OHPC in women are mixed however, with one finding weak effects with 100 mg/day whereas another found that doses of 250 to 1,000 mg produced no effects. As a result of its low oral potency, OHPC has not been used by the oral route and has instead been administered by intramuscular injection.