Although the elimination half-life of intramuscular OHPC in oil solution in non-pregnant women is about 8 days, the elimination half-life of intramuscular medroxyprogesterone acetate in microcrystalline aqueous suspension in women is around 50 days. OHPC is also to some degree less potent than the more closely related ester hydroxyprogesterone acetate (OHPA; 17α-hydroxyprogesterone acetate).17α-Hydroxyprogesterone (OHP) has weak progestogenic activity, but C17α esterification results in higher progestogenic activity. Of a variety of different esters, the caproate (hexanoate) ester was found to have the strongest progestogenic activity, and this served as the basis for the development of OHPC, as well as other caproate progestogen esters such as gestonorone caproate. OHPC is a much more potent progestogen than 17α-hydroxyprogesterone, but does not have as high of affinity for the PR as progesterone. OHPC has about 26% and 30% of the affinity of progesterone for the human PR-A and PR-B, respectively. The medication was no more efficacious than progesterone in activating these receptors and eliciting associated gene expression in vitro. Antigonadotropic effects
Due to activation of the PR, OHPC has antigonadotropic effects, or produces suppression of the hypothalamic–pituitary–gonadal axis, and can significantly suppress gonadotropin secretion and gonadal sex hormone production at sufficiently high doses. One study found that OHPC by intramuscular injection at a dosage of 200 mg twice weekly for the first two weeks and then 200 mg once weekly for 12 weeks did not significantly influence urinary excretion of estrogens, luteinizing hormone, or follicle-stimulating hormone in men with benign prostatic hyperplasia.
Mechanism
In method of action, the preparation is identical to that of caffeine base as the citrate counter ion dissociates in water. Doses of caffeine citrate, due to the added weight of the citrate moiety, are understandably higher than with caffeine base, i.e., it takes a larger dose to get the same amount of caffeine. The ratio of therapeutic doses of caffeine base to its citrate salt is typically 1:2. Dosing should therefore be clearly distinguished. Manufacture
The drug is prepared by combining anhydrous caffeine with citric acid monohydrate and sodium citrate dihydrate. Caffeine citrate cocrystals can take on at least two anhydrous polymorphs. References
External links
"Caffeine citrate". Drug Information Portal. U.S. National Library of Medicine. "Caffeine Citrate (CUI C0054436)". NCI Metathesaurus.