Etonogestrel is a medication which is used as a means of birth control for women. It is available as an implant placed under the skin of the upper arm under the brand names Nexplanon and Implanon. It is a progestin that is also used in combination with ethinylestradiol, an estrogen, as a vaginal ring under the brand names NuvaRing and Circlet. Etonogestrel is effective as a means of birth control and lasts at least three or four years with some data showing effectiveness for five years. Following removal, fertility quickly returns.
Side effects of etonogestrel include menstrual irregularities, breast tenderness, mood changes, acne, headaches, vaginitis, and others. Etonogestrel is a progestin, or a synthetic progestogen, and hence is an agonist of the progesterone receptor, the biological target of progestogens like progesterone. It works by stopping ovulation, thickening the mucus around the opening of the cervix, and altering the lining of the uterus. It has very weak androgenic and glucocorticoid activity and no other important hormonal activity.
Etonogestrel was patented in 1972 and introduced for medical use in 1998. It became available in the United States in 2006. Etonogestrel implants are approved in more than 90 countries and used by about three million women globally as of 2010.
A closely related and more widely known and used progestin, desogestrel, is a prodrug of etonogestrel in the body.
Medical uses
Etonogestrel is used in hormonal contraception in form of the etonogestrel contraceptive implant and the contraceptive vaginal ring (brand names NuvaRing, Circlet), the latter in combination with ethinylestradiol.
Etonogestrel birth control implants are a type of long-acting reversible contraception, which has been shown to be one of the most effective form of birth control. The failure rate of the implants is 0.05% for both perfect use and typical use because the method requires no user action after placement. Studies of one type, which include over 2,467 women-years of exposure, found no pregnancies.
Other studies have found some failures with this method, some attributed to failures of the method itself and others to improper placement, drug interactions, or conception prior to method insertion.
In comparison, tubal sterilization has a failure rate of 0.5% and IUDs have a failure rate of 0.2–0.8%. A single implant is approved for three years with data showing effectiveness for five years.
Contraindications
Women should not use implants if they:
are, or think they are, pregnant
are allergic to etonogestrel
have vaginal bleeding that has not been explained
have some forms of severe liver disease.
Women should not use combined hormone contraceptives (CHC) if they have migraines with auras.
A full list of contraindications can be found in the WHO Medical Eligibility Criteria for Contraceptive Use 2015 and the CDC United States Medical Eligibility Criteria for Contraceptive Use 2016.
Side effects
Irregular bleeding and spotting: Many women will experience some type of irregular, unpredictable, prolonged, frequent, or infrequent bleeding. Some women also experience amenorrhea. For some women, prolonged bleeding will decline after the first three months of use. However, other women may experience this bleeding pattern through all five years of use. While these patterns are not dangerous, they are the most common reason that women give for discontinuing the use of the implant. After removal, bleeding patterns return to previous patterns in most women.
Insertion complications: Some minor side effects such as bruising, skin irritation, or pain around the insertion site are common. However, there are some rare complications that can occur, such as infection or expulsion. In some cases, a serious complication occurs when the provider fails to insert, and the rod is left in the inserter. An Australian study reported 84 pregnancies as a result of such failure.
Migration: Although very rare, the rod can sometimes move slightly within the arm. This can make removal more difficult. It is possible that insertion in the same site as a previous implant increases the likelihood of migration. Rods can be located only through high-frequency ultrasound or magnetic resonance imaging (MRI). It can be located using traditional X-ray or CT-scan because of the inclusion of barium sulphate. There have been rare reports of implants having reached the lung via the pulmonary artery. Correct subdermal insertion over the triceps muscle reduces the risk of these events.