title: Levonorgestrel concentrations during use of levonorgestrel rod (LNG ROD) implants.
abstract: 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.
authors.affiliation: Center for Biomedical Research, Population Council, New York, NY 10021, USA.
authors.forename: I
authors.initials: I
authors.lastname: Sivin
authors.forename: P
authors.initials: P
authors.lastname: Lähteenmäki
authors.forename: S
authors.initials: S
authors.lastname: Ranta
authors.forename: P
authors.initials: P
authors.lastname: Darney
authors.forename: C
authors.initials: C
authors.lastname: Klaisle
authors.forename: L
authors.initials: L
authors.lastname: Wan
authors.forename: D R
authors.initials: DR
authors.lastname: Mishell
authors.forename: M
authors.initials: M
authors.lastname: Lacarra
authors.forename: O A
authors.initials: OA
authors.lastname: Viegas
authors.forename: P
authors.initials: P
authors.lastname: Bilhareus
authors.forename: S
authors.initials: S
authors.lastname: Koetsawang
authors.forename: M
authors.initials: M
authors.lastname: Piya-Anant
authors.forename: S
authors.initials: S
authors.lastname: Diaz
authors.forename: M
authors.initials: M
authors.lastname: Pavez
authors.forename: F
authors.initials: F
authors.lastname: Alvarez
authors.forename: V
authors.initials: V
authors.lastname: Brache
authors.forename: K
authors.initials: K
authors.lastname: LaGuardia
authors.forename: H
authors.initials: H
authors.lastname: Nash
authors.forename: J
authors.initials: J
authors.lastname: Stern
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000704:Analysis of Variance; D001835:Body Weight; D003271:Contraceptive Agents, Female / Q000008:administration & dosage* / Q000097:blood* / Q000592:standards; D004343:Drug Implants; D005260:Female; D006801:Humans; D016912:Levonorgestrel / Q000008:administration & dosage* / Q000097:blood* / Q000592:standards; D011247:Pregnancy; D018873:Pregnancy Rate; D013997:Time Factors
chemical_list: D003271:Contraceptive Agents, Female; D004343:Drug Implants; D016912:Levonorgestrel