Medroxyprogesterone acetate (MPA) plasma levels after oral and intramuscular administration in a long-term study.

In a long-term study (1 year) the plasma concentration of medroxyprogesterone acetate (MPA, Depo-Provera, Provera, Upjohn) was measured in 30 patients with endometrial carcinoma treated with MPA in the following dosages: 1) MPA 1 000 mg i.m. weekly; 2) MPA 1 000 mg i.m. once every second week, and; 3) MPA 100 mg orally twice daily. In the orally treated group the blood samples were taken just before the next tablet. The plasma concentration in the orally treated group rapidly reached steady state, while the i.m. treated group showed gradually increasing levels that had a tendency to level off after 6 months. The mean concentration at the end of the year was about three times higher for MPA 1000 mg i.m. weekly than for MPA 100 mg orally twice daily. This does not take into consideration the peak MPA level that occurs 2-4 hours after each tablet. MPA i.m. has a very good depot effect, with release of MPA from the injection site for up to 9 months. The steady initial increase in MPA plasma concentration seen in the i.m. treated groups is probably due to the additions of new depots rather than accumulation in the body generally.