The plasma concentration of medroxyprogesterone acetate and ovarian function during treatment with medroxyprogesterone acetate in 5 and 10 mg doses.

Peripheral plasma levels of medroxyprogesterone acetate (MPA) were determined by radioimmunoassay in 5 women after oral administration of 5 and 10 mg medroxyprogesterone acetate daily. Peak levels of MPA in plasma were recorded within 1 - 3 hours of taking the tablet, which indicates a rapid absorption from the gastro-intestinal tract. The levels of medroxyprogesterone acetate 12 hours after taking of the 5 mg tablet remained constant throughout the 8 weeks of study. Peripheral plasma levels of estradiol and progesterone were determined throughout treatment. The estradiol levels indicated development of follicles in 7 out of 10 treatment months in the 5 mg group, and in 3 of the subjects treated with 10 mg MPA. The progesterone levels in those women treated with 5 mg MPA showed normal luteal concentration values in 2 out of 10 treatment months. No woman treated with 10 mg MPA had an increase in progesterone during the 21-day period of treatment. The results obtained in this study suggest that 10 mg MPA daily will inhibit ovulation but 5 mg is not sufficient to inhibit ovulation in all women.