Johansson Elof, Vivian Brache, Frank Alvarez, Anibal Faundes, Leila Cochon, Sirpa Ranta, Mark Lovern, and Narender Kumar. 2002. “Pharmacokinetic study of different dosing regimens of levonorgestrel for emergency contraception in healthy women,” Human Reproduction 17(6):1472–1476.

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.

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