Pharmacokinetic study of different dosing regimens of levonorgestrel for emergency contraception in healthy women.
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 approximately 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.
Johansson
Elof
E
Center for Biomedical Research, The Population Council, New York, NY, USA.
Brache
Vivian
V
Alvarez
Frank
F
Faundes
Anibal
A
Cochon
Leila
L
Ranta
Sirpa
S
Lovern
Mark
M
Kumar
Narender
N
D000293:Adolescent; D000328:Adult; D003283:Contraceptives, Postcoital, Synthetic / Q000008:administration & dosage* / Q000493:pharmacokinetics*; D004334:Drug Administration Schedule; D005260:Female; D006801:Humans; D016912:Levonorgestrel / Q000008:administration & dosage* / Q000097:blood / Q000493:pharmacokinetics*; D008875:Middle Aged; D012738:Sex Hormone-Binding Globulin / Q000378:metabolism
D003283:Contraceptives, Postcoital, Synthetic; D012738:Sex Hormone-Binding Globulin; D016912:Levonorgestrel