Clinical Review


Author and Disclosure Information

Implanon approved … Why the FDA removed ParaGard’s parity rule … Plan B does not promote high-risk behavior



Three new developments this year stand to make a difference in the high rate of unintended pregnancies in the United States. Increased use of highly effective, long-acting, user-independent methods is an effective way to lower the rate of unintended pregnancies in couples using contraception. Two such methods are the contraceptive implant and the intrauterine contraceptive. Emergency contraception is an effective way to reduce the risk of unintended pregnancy after failure of a contraceptive method or unprotected or forced sex. A randomized trial showed that direct access to EC does not increase high-risk behavior.

Half of pregnancies are unintended

  • The United States has one of the highest rates of unintended births among industrialized countries.
  • Of the 6 million pregnancies each year in the US, nearly 3 million are unintended, resulting in 1.4 million unintended births and 1.3 million abortions.
  • Half of these unintended pregnancies are due to failure or incorrect or inconsistent use of a contraceptive method.1


1. Contraception Counts: Ranking State Efforts. New York: Guttmacher Institute; February 2006.

Implanon essentials: How it works and what to tell patients

The single-rod implant (Implanon) is a new, highly effective, long-acting, rapidly reversible contraceptive, approved by the FDA, July 17, 2006.

A new single-rod implant that provides highly effective contraception for up to 3 years is expected to be widely available in the United States in 2007. Once inserted, Implanon is independent of user compliance and is rapidly effective and reversible. It is in use worldwide in more than 30 countries since 1998.

The new device is a nonbiodegradable 40 × 2.0 mm rod of 40% ethylene vinyl acetate (EVA) and 60% etonogestrel (ENG) covered with a rate-controlling EVA membrane.

The rod contains 68 mg of ENG, initially absorbed by the body at a rate of 60 μg/day, slowly declining to 30 μg/day after 3 years of use.2 Steady release of ENG into the circulation avoids first-pass effects on the liver.

Manufacturer-sponsored training: Call 1-877-IMPLANON

Before clinicians can order the implant, they must undergo training sponsored by the manufacturer, Organon. To take part in the training, which is set to begin in August, call 1-877-IMPLANON.

How the implant works

Ovarian and cervical mechanisms, which function prior to fertilization, provide high contraceptive efficacy.

Ovulation is suppressed. The ENG implant, unlike previous levonorgestrel-containing implants, works primarily by suppressing ovulation.3 ENG alters the hypothalamic–pituitary–ovarian axis and down-regulates the luteinizing hormone surge, which is required to support the production, growth, and maturation of ovarian follicles.

Ovulation returns rapidly after removal of the implant.3

Cervical mechanisms also prevent fertilization. Anti-estrogenic actions of ENG make the cervical mucus viscous, scanty, and impenetrable by sperm.

Cost-effectiveness depends on long-term use; early removal negates this benefit. At press time, the manufacturer had not released the price of Implanon.

Lack of protection against sexually transmitted infections is a disadvantage of the ENG implant, as well as all nonbarrier contraceptive methods.

Discontinuation rates have varied by region, but are usually due to bleeding pattern changes.

  • In an international multicenter trial, 31% discontinued by 2 years and only 6% discontinued in the third year.4 Again, the most common reason was irregular bleeding.
  • In a US series, 49% discontinued by 2 years. The most common reason was bleeding pattern changes (13%).5 The rate of discontinuation was highest during the first 8 months.

What to tell patients. To improve continuation, counseling should strongly stress the expected change in bleeding patterns.

Clinical trials

Outstanding efficacy. In an international multicenter trial, there were no intrauterine or ectopic pregnancies in a total of 1,200 woman-years (15,000 cycles of exposure, 2,000 of which were in the third year of use).4 The Pearl index was 0 (95% CI 0.0–0.2).4 In the US series, after a total exposure of 474 woman-years (6,186 cycles), no intrauterine or ectopic pregnancies were observed.5 It should be noted that phase III data from Indonesia were retracted by the manufacturer in 2004.6 The 2 trials noted above included a total of 965 women and were not included in this retraction.

Reasons for failures. Pregnancies were noted from postmarketing data in Australia; most of these pregnancies resulted from either incorrect timing at the initial insertion or failure to insert the implant. Based on the Australian phase IV data, with 204,486 devices inserted, the failure of the method itself was estimated to be 1 per 1,000 insertions.7 Implanon may be less effective in obese women or, as the Australian experience showed, with concomitant use of drugs that stimulate the liver’s cytochrome metabolism of steroids, such as some antibiotics (eg, rifampin) or anticonvulsants (eg, phenytoin).


Next Article: