The pharmacokinetics of levonorgestrel and ethynylestradiol in women: studies with Ovran and Ovranette.

Abstract A radioimmunoassay for levonorgestrel (Ng), which is applicable to plasma samples obtained from women who have taken a combination type oral contraceptive, has been developed and fully validated. Plasma concentrations of Ng rise to a peak of 3.6 ng/ml after an oral dose of 150 μg and to 5.0 ng/ml after a 250 μg dose. Following the intravenous administration of Ng, plasma concentrations of the steroid decline biexponentially with mean half-lives of 0.76 and 11.55 hours. Comparison of the results of the intravenous and oral administration of the steroid show a mean systemic bioavailability of 89% after the 150 μg dose and 99% after a 250 μg dose. This difference was not statistically significant. The values for volume of distribution were approximately half and the values for plasma clearance three times less than that previously reported for norethindrone. The plasma ethynylestradiol levels were also measured following administration of 30μg both intravenously and orally. The bioavailability and kinetics were similar to that previously reported for a 50μg dose. The peak values after oral dosing were 103 pg/ml and were reached by 1.0 hour in all subjects.