Subdermal implants are contraceptive systems that release low, stable amounts of synthetic progestins from Silastic or other materials for periods of months to several years. Unlike other hormonal delivery systems, they do not cause unnecessary peaks in progestin levels and do not use estrogens, and thus their health risks are minimal. Norplant has been studied more extensively than any other subdermal contraceptive implant. More than 60,000 women have participated in clinical trials, which demonstrated that this approach is one of the most effective reversible contraceptive methods available (1% pregnancy rate in 5-year users). The implant also reduces the incidence of ectopic pregnancy to a level much below noncontraceptive users and about equivalent to TCu380A intrauterine device users. Exposure to the sustained, low dose of levonorgestrel delivered by Norplant has shown only minor metabolic changes. Side effects are minor but often bothersome, causing some discontinuation of the method. First-year continuation rates range from 76% to 90%. Fertility return after discontinuation is prompt. Difficulty in removal of the implant capsules by the less experienced practitioner has motivated researchers to develop systems that are easier to use, less obvious under the skin, and biodegradable. The Norplant 2 system is faster, easier, and less painful to insert and remove. Implants under investigation release desogestrel and other progestins; Capronor and subdermal norethindrone pellets are biodegradable systems.
PIP: Subdermal contraceptive implant systems release low, stable amounts of progestins. Norplant has been used by more than 3 million women, and more than 60,000 have participated in clinical trials. Insertion requires 5-minutes of careful work. The mode of action is the suppression of ovulation by levonorgestrel. Norplant is 99% effective over 5-years of use. There are disagreeable side effects, however, including acne, weight gain, and menstrual irregularity, which is the greatest cause of discontinuation. First-year continuation rates range from 76-90%, and fertility returns promptly upon removal (which can be done in 5 minutes but may take as long as an hour). Implants which would be less obvious subdermally and which would biodegrade are under investigation. Other favorable features would be disposable insertion devices and the use of less androgenic progestins to reduce side effects. Norplant 2 implants, currently regarded as a 3-year system, offer some advantages such as being less conspicuous and easier to insert and remove and are under study for 5-year efficacy determination. Implants releasing desogestrel and other progestins are undergoing clinical trials which are revealing bleeding irregularities similar to Norplant but a possible reduction in other side effects. Degradable implants must be removable during their active life if the user desires. The Capronor implant, which biodegrades, is quicker and easier to remove than Norplant but has the same side effects. Biodegradable subdermal pellets, composed of 10% pure cholesterol and 90% norethindrone, are the size of a grain of rice. Comparative trials are underway to determine the size, number of pellets, and cholesterol/hormone ratio to obtain serum norethindrone levels above the contraceptive threshold but lower than oral contraceptives. Disrupted bleeding patterns in the first few months return to normal. The 4-pellet system has been most effective in preventing pregnancy, but removal can be complicated by fracture of the pellets. These systems under investigation will likely address all of the problems of inserts except insertion and bleeding.