Contraceptive efficacy, pharmacokinetics, and safety of Annuelle biodegradable norethindrone pellet implants.

Objective: To evaluate the contraceptive efficacy, pharmacokinetics, and safety of two formulations of Annuelle (Endocon, Inc., South Walpole, MA) biodegradable norethindrone (NET) SC pellet implants.
Design: Prospective observational study.
Setting: Two clinical sites in the United States.
Patient(s): Thirty-nine healthy, fertile, sexually active women.
Intervention(s): Nineteen women received a four-pellet system containing 174 mg NET; 20 women received a five-pellet system containing 266.5 mg NET.
Main Outcome Measure(s): Contraceptive efficacy, median serum NET levels, adverse events.
Result(s): No pregnancies were observed in 293 woman-months in the four-pellet group or in 375 woman-months in the five-pellet group. An initial burst in median serum NET levels occurred in the first 24 hours postinsertion followed by a steady decline over the next 3 years. Norethindrone levels varied considerably among women. The main side effect was bleeding abnormalities, which persisted in half the participants for up to 2 years. No serious adverse events were reported that were related to the pellets. Pellet insertion and removal generally were uncomplicated.
Conclusion(s): Annuelle shows potential as an effective, safe contraceptive with distinct advantages over other long-acting agents, because it is biodegradable but can be removed if problems arise or if fertility is desired.