Medroxyprogesterone was originally approved by the FDA in 1959. Medroxyprogesterone inhibits secretion of pituitary gonadotropins, which prevents follicular maturation and ovulation. The drug converts a proliferative endometrium into a secretory state. The mode of action against certain cancers has not been determined. Progestins also can demonstrate estrogenic, anabolic, and androgenic activity.
Progestins are also mild, direct stimulants of the respiratory center.
During pregnancy and the luteal phase of the menstrual cycle, women can hyperventilate and become hypocapnic due to elevated concentrations of endogenous progestins. Therapeutically, medroxyprogesterone has been used successfully in patients with COPD and hypercapnia, in patients with Pickwickian syndrome, and in patients with sleep apnea. Oral bioavailability is not known. Following a single IM dose, concentrations increase progressively for 3 weeks, then begin to decrease exponentially to undetectable levels at 120-200 days following the injection. The half-life following IM administration of the depot form is 50 days.