Pharmacokinetics of gestodene and ethinyl estradiol after oral administration of a monophasic contraceptive.

The pharmacokinetic and protein-binding properties of gestodene and ethinyl estradiol have been investigated after single and multiple dosing in several studies in 83 healthy, young women. After oral administration, gestodene is completely absorbed and bioavailable and exhibits dose-linear pharmacokinetics. During long-term pill use, serum levels of gestodene were four to five times higher than after single administration, showing a periodic increase from day 1 to day 10 during each cycle. Ultrafiltration studies revealed that 75.3% of total serum gestodene is bound to sex hormone-binding globulin, 24.1% is bound to albumin, and only 0.6% is not protein bound. Thus gestodene levels during steady state are explained by an increase in sex hormone binding-globulin as a result of concomitant administered ethinyl estradiol and a specific binding of gestodene to this protein. Serum levels of ethinyl estradiol during single and multiple administration were identical and were not different from those observed with another preparation containing 30 micrograms of ethinyl estradiol.