Levonorgestrel concentrations during use of levonorgestrel rod (LNG ROD) implants

Irving Sivin, Pekka Lähteenmäki, Sirpa Ranta, Philip Darney, Cindy Klaisle, Livia Wan, Daniel R. Mishell, Maria Lacarra, Osborn A.C. Viegas, Prapas Bilhareus, Suporn Koetsawang, Manee Piya-Anant, Soledad Diaz, Margarita Pavez, Francisco Alvarez, Vivian Brache, Katherine LaGuardia, Harold Nash, Janet Stern

Research output: Contribution to journalArticlepeer-review

52 Scopus citations


In a three-year randomized trial that included 398 women, blood samples were collected for the purpose of assaying levonorgestrel concentrations in women using a new two-rod contraceptive implant system or an earlier implant formulation, Norplant®-2 implants. Sample collection was at 1, 3, 6, 9, and 12 months after placement and semiannually thereafter through three years. Resulting assays and analyses showed that levonorgestrel concentrations of each implant formulation decreased significantly with time after placement, with increasing body weight, and with ponderal index. In the third year, several measures indicated that concentrations of the contraceptive drug were higher in women using the LNG ROD implants than in users of the original formulation. No pregnancies occurred among women in either group in the three years. This study provides evidence that the minimum levonorgestrel concentration needed to protect against pregnancy is below 200 pg/ml, and possibly is below 175 pg/ml.

Original languageEnglish
Pages (from-to)81-85
Number of pages5
Issue number2
StatePublished - Feb 1997
Externally publishedYes


  • contraception
  • implants
  • levonorgestrel concentrations
  • rod implants


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