Contraception
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Randomized Controlled Trial Comparative Study Clinical Trial
Pharmacokinetics of levonorgestrel and ethinylestradiol in 9 women who received a low-dose oral contraceptive over a treatment period of 3 months and, after a wash-out phase, a single oral administration of the same contraceptive formulation.
The pharmacokinetics of levonorgestrel (LNG) and ethinylestradiol (EE2) were determined in 9 healthy women (age 23 to 42 years), during a treatment period of three months with a low-dose oral contraceptive, containing 0.15 mg LNG together with 0.03 mg EE2 (Microgynon). After a wash-out period of 3 months, 8 of these women received a single administration of the same formulation. The results showed that there was an increase in serum trough levels of LNG, reaching steady-state in the second half of each treatment cycle. ⋯ An about 50% reduction in total and unbound clearance of LNG was observed during chronic treatment, as compared to single dose administration. Increased SHBG binding capacity and a reduced hepatic metabolic capacity were discussed as possible causes of accumulating LNG concentrations in the serum. On the last day of treatment cycles one and three, the AUC(0-24h) values of EE2 were 728 +/- 314 and 778 +/- 318 pg x ml-1 x h, respectively, and were in keeping with data reported from others.