Serum Medroxyprogesterone Acetate (MPA) Concentrations and Ovarian Function Following Intramuscular Injection of Depo-MPA

A sensitive radioimmunoassay measuring serum medroxyprogesterone acetate (MPA) has been developed in order to measure and correlate serum MPA concentrations and ovarian function in women following im administration of depo-MPA (DMPA), employing goat anti-MPA-3-(O-carboxymethyl) oxime-bovine serum albumin and MPA-3-(O-carboxymethyl) imino-125I-iodohistamine. In the 3 women studied, im injection of 150 mg of DMPA yielded brief initial serum MPA concentrations ranging from 1.5 to 3 ng/ml for a few days. Serum MPA concentrations gradually declined and remained relatively constant at about 1 ng/ml for 2 to 3 months, declined gradually thereafter reaching 0.2 ng/ml during the 6th month and became undetectable (<0.02 ng/ml) about 7½ to 9 months following administration. Serum estradiol remained at early to midfollicular phase levels for 4 to 6 months after DMPA injection and rose to preovulatory levels when serum MPA levels fell below 0.5 to 0.25 ng/ml. Ovulation, however, as evidenced by serum progesterone conc...