Clinical evaluation of an improved injectable microcapsule contraceptive system

Pharmacokinetics and pharmacodynamics of a long-acting injectable microcapsule, poly(DL-lactide-co-glycolide), delivery system were tested in 10 women. Two doses (75 or 100 mg of norethindrone) were administered by intramuscular injection. Treatment suppressed ovarian function and inhibited ovulation for 3 months in all subjects. Levels of norethindrone in subjects who received the 100 mg dose were proportionately higher than those in subjects who received the 75 mg dose. Subsequent to the injection, there was a rapid rise in the serum levels of norethindrone followed by a gradual decline until 8 to 10 weeks. Between 10 and 20 weeks after treatment, there was a secondary rise and fall in the serum levels of norethindrone. Treatment caused suppression of the endometrium for 3 months, and, except for spotting and irregular menstrual cycles, there were no adverse side effects. Treatment had no significant effect on serum lipids.