Phase II clinical study of implanted norethindrone pellets for longterm contraception in women

The use of subcutaneously implanted fused pellets made of norethindrone (NET) and pure cholesterol was evaluated as a means of longterm contraception (6 months) in 81 women at three clinics. Fifty-one women used pellets containing 103 mg NET (3 pellets) and 30 women used pellets containing 138 mg NET (4 pellets). There were no serious local reactions to the pellets. There was no apparent initial NET burst effect and serum NET levels remained constant over the follow-up period. Median NET serum levels were similar (p>0.10) for women who used 3 or 4 pellets. Most menstrual cycles showed no evidence of ovulation (i.e., serum progesterone levels did not exceed 5 ng ml-1: the proportion of women with serum progesterone levels greater than 5 ng ml-1 was lower with the 4 pellet dose. For women who used either 3 or 4 pellets there was an increase (p<0.05) in the number of days of bleeding or spotting. There was a decrease in the incidence of dysmenorrhea (p<0.05) for both groups of women. There was a low incidence of side effects and complications. There were two pregnancies; both occurred in women using 3 pellets.