A pharmacokinetic study with a low-dose oral contraceptive containing 20 microg ethinylestradiol plus 100 microg levonorgestrel

Abstract

This study investigated the pharmacokinetics of a dose-reduced oral contraceptive containing 20 microg ethinylestradiol (EE) + 100 microg levonorgestrel (LNG) in 18 young, healthy females. Serum levels of EE and LNG were determined after single and repeated daily oral administration over three treatment cycles, each consisting of 21 treatment days followed by a 7-day treatment-free period. Additionally, the time courses of sex hormone-binding globulin (SHBG), corticoid-binding globulin (CBG) and total and free testosterone serum levels were analyzed. Both active ingredients were rapidly absorbed and maximum concentrations in serum were reached between, on average, 1 and 2 h after single and multiple administrations, respectively. Concentrations of EE increased during repeated daily administration. An approximate two-fold accumulation was calculated based on the comparison of EE area under the curve (AUC) (0-24 h) values determined after the first and the last tablet administration within a treatment cycle. LNG serum concentrations also increased during repeated daily administration, reaching steady-state levels after about 11 days. Based on the comparison of AUC (0-24 h) values determined after the first and the last tablet administration, LNG accumulated approximately by a factor of 3 within a treatment cycle. Steady-state pharmacokinetics of LNG were similar at the end of the first and the third treatment cycles, indicating no further accumulation of LNG beyond a treatment cycle under long-term use of this combined oral contraceptive. The clearance and volume of distribution of LNG decreased and the terminal half-life increased after repeated daily administration, compared with single administration. These effects have also been reported for other LNG/EE combinations. SHBG serum concentrations increased during repeated daily intake by, on average, 1.5-1.6-fold, and for CBG, an average increase of 1.4-1.8-fold was found. Although free testosterone concentrations declined during repeated daily administration by about 40%, total testosterone remained relatively unchanged at a low level. In conclusion, the pharmacokinetics of EE and LNG determined in the present study were in good agreement with those previously reported for 30 microg EE + 150 microg LNG, taking the 33% dose reduction into account.