SUBDERMAL CONTRACEPTIVE IMPLANTS

Subdermal contraceptive implants involve the delivery of a steroid pro gestin from polymer capsules or rods placed under the skin. The hormon e diffuses out slowly at a stable rate, providing contraceptive effect iveness for 1-5 years. The period of protection depends upon the speci fic progestin and the type of polymer. Advantages of progestin implant s include long term contraceptive action without requiring the user's or provider's attention, low dose of highly effective contraception wi thout the use of estrogen, and fertility is readily reversible after t he removal of implants. The levonorgestrel implant Norplant R system i s the only one that has been approved for distribution. The contracept ive efficacy of Norplant is the highest observed amongst the most effe ctive methods with an annual pregnancy rate of 0.2 during the first an d second year and 1.1 on the fifth year. Menstrual problems are the ma in 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 eff ects. Norplant-2 was designed to release the same dose of progestin fr om 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. Ble eding irregularities occurred in 20-30% of the women but there were on ly four terminations because of bleeding problems. A multricentric stu dy is ongoing with a newly designed 3-keto-desogestrel implant named I mplanon, which releases approx. 60 mu g/day of the hormone. The object ives of this study are to assess contraceptive efficacy, safety and ac ceptability of Implanon. Another multricentric study is ongoing with U niplant, which releases nomegestrol acetate with a duration of action for only 1 year. The objectives of the trial are to study the endocrin e profile of Uniplant users and to evaluate the efficacy and acceptabi lity of the method.