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

To evaluate the contraceptive efficacy, pharmacokinetics, and safety of two formulations of Annuelle (Endocon, Inc., South Walpole, MA) biodegradable norethindrone (NET) SC pellet implants.

Prospective observational study.

Two clinical sites in the United States.

Thirty-nine healthy, fertile, sexually active women.

Nineteen women received a four-pellet system containing 174 mg NET; 20 women received a five-pellet system containing 266.5 mg NET.

Contraceptive efficacy, median serum NET levels, adverse events.

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.

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.