Subdermal contraceptive implants involve the delivery of a steroid progestin from polymer capsules or rods placed under the skin. The hormone diffuses out slowly at a stable rate, providing contraceptive effectiveness for 1-5 years. The period of protection depends upon the specific progestin and the type of polymer. Advantages of progestin implants include long term contraceptive action without requiring the user's or provider's attention, low dose of highly effective contraception without the use of estrogen, and fertility is readily reversible after the removal of implants. The levonorgestrel implant Norplant R system is the only one that has been approved for distribution. The contraceptive efficacy of Norplant is the highest observed amongst the most effective methods with an annual pregnancy rate of 0.2 during the first and second year and 1.1 on the fifth year. Menstrual problems are the main reason for the discontinuation of Norplant and 9% of women stopped using it during the first year of treatment. Other implants are still under development trying to simplify the method by reducing the number of units and to introduce other progestins that may minimize side effects. Norplant-2 was designed to release the same dose of progestin from only two covered rods. Evaluation of 1400 women enrolled, indicates that over 2 years the cumulative pregnancy rate is below 0.5 per 100 women. There are three single implants under development: Nestorone, 3-Keto-desogestrel and Uniplant that are expected to be effective for 1-2 years. Phase II clinical trials with Nestorone have been completed and no pregnancies have been observed in 1570 woman-months of use. Bleeding irregularities occurred in 20-30% of the women but there were only four terminations because of bleeding problems. A multricentric study is ongoing with a newly designed 3-keto-desogestrel implant named Implanon, which releases approx. 60 micrograms/day of the hormone. The objectives of this study are to assess contraceptive efficacy, safety and acceptability of Implanon. Another multricentric study is ongoing with Uniplant, which releases nomegestrol acetate with a duration of action for only 1 year. The objectives of the trial are to study the endocrine profile of Uniplant users and to evaluate the efficacy and acceptability of the method.
PIP: Subdermal contraceptive implants deliver progestin from polymer capsules or rods placed under the skin. Diffusing slowly from the polymer containers at a stable rate, the hormone provides contraception for 1-5 years, with the period of protection conferred dependent upon the specific progestin and type of polymer employed. Once inserted, the device allows a woman to have sexual intercourse over a certain period of time without any significant risk of becoming pregnant. Protection is ensured with a low drug dosage and no estrogen, and fertility is readily reversible once the implants are removed. The levonorgestrel implant Norplant R is the only subdermal contraceptive implant system approved for distribution. Annual pregnancy rates using Norplant are extremely low. Menstrual problems are the main reason why women discontinue using Norplant. Research is ongoing to reduce the number of implanted units and to introduce other progestins which may minimize side effects. Norplant-2 was designed to release the same dose of progestin from only two covered rods. Nestorone, 3-Keto-desogestrel, and Uniplant are single implants under development which are expected to be effective for 1-2 years. Completed phase II clinical trials with Nestorone found no pregnancies in 1570 woman-months of use, although bleeding irregularities occurred in 20-30% of women. A multicenter study is ongoing with a newly-designed 3-keto-desogestrel implant named Implanon, as well as another multicenter study with Uniplant, an implant which releases nomegestrol acetate with a one-year duration of action.