Multicenter clinical trial of implanted norethindrone pellets for long-acting contraception in women. Program for Applied Research on Fertility Regulation.

Long-acting, biodegradable, subcutaneous implants of fused pellets composed of norethindrone (NET) and pure cholestrol were evaluated in 50 healthy, normally menstruating volunteers from five clinics. Evaluation of serum NET levels indicated a steady release rate over the 6-cycle follow-up period. There were no serious local reactions to the pellets. Menstrual cycle length remained unchanged, but the incidence of intermenstrual bleeding and/or spotting was higher during the initial 2-3 months of pellet use. Following pellet removal menstrual cycle parameters returned to their pre-pellet implantation values. Serum gonadotropin assays indicated the incidence of ovulatory cycles increased over the follow-up period. No significant changes in serum lipoproteins, SMAC-12 or enzyme profiles were observed. Although women were advised to use additional methods of contraception, three became pregnant while using the implants. Fibrous tissue was noted to form around the pellets, thus limiting the release of NET. Additional trials of higher NET doses are being evaluated.