Human Reproduction, Vol. 17, No. 6, 1472-1476,
June 2002
© 2002 European Society of Human Reproduction and Embryology
Pharmacokinetic study of different dosing regimens of levonorgestrel for emergency contraception in healthy women
1 Center for Biomedical Research, The Population Council, New York, NY, USA, 2 PROFAMILIA, Santo Domingo, Dominican Republic, 3 CEMICAMP, Campinas, SP, Brasil, 4 Steroid Research Laboratory, Institute of Biomedicine, University of Helsinki, Helsinki, Finland and 5 Pharsight Corporation, Cary, NC, USA
BACKGROUND: Levonorgestrel (LNG) is a commonly used progestin for emergency contraception; however, little is known about its pharmacokinetics and optimal dose for use. METHODS: Serum levels of LNG and sex hormone-binding globulin (SHBG) were measured in five women who received three different regimens: A: 0.75 mg LNG twice with a 12 h interval; B: 0.75 mg twice with a 24 h interval; and C: 1.50 mg in a single dose, with a washout period of 28 days between each treatment. Blood samples were taken before pill intake and at 1, 2, 4, 8 and 12 h after each dose, every 12 h up to day 4 and every 24 h until day 10. LNG and SHBG were measured in all samples. RESULTS: Maximum LNG concentrations were of ~27 nmol/l for treatments A and B, and close to 40 nmol/l for treatment C. The area under the curve was significantly higher for treatment C during the first 12 h, and significantly lower for treatment B during the first 24 h. After 48 h and up to 9 days from onset of treatment, serum LNG levels were similar in all three regimens. SHBG levels remained stable for 24 h, decreasing to 60% of the initial value from day 5 until day 10, with no difference between regimens. CONCLUSIONS: The similarity of LNG serum levels obtained with one single dose of 1.5 mg or two doses of 0.75 mg with a 12 h interval justify a clinical comparison of these two regimes.
Key words: emergency contraception/levonorgestrel/pharmacokinetics/SHBG
6 To whom correspondence should be addressed at: PROFAMILIA, Biomedical Research Department, P.O. Box 1053, Santo Domingo, Dominican Republic. E-mail: biomedica{at}codetel.net.do
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