Combination oral contraceptives act by suppression of gonadotropins. Although the primary mechanism of this action is inhibition of ovulation, other alterations include changes in the cervical mucus (which increase the difficulty of sperm entry into the uterus) and the endometrium (which reduce the likelihood of implantation).

Receptor binding studies, as well as studies in animals, have shown that etonogestrel, the biologically active metabolite of desogestrel, combines high progestational activity with minimal intrinsic androgenicity (91,92). The relevance of this latter finding in humans is unknown.

Pharmacokinetics

Absorption

Desogestrel is rapidly and almost completely absorbed and converted into etonogestrel, its biologically active metabolite. Following oral administration, the relative bioavailability of desogestrel compared to a solution, as measured by serum levels of etonogestrel, is approximately 100%. Mircette® (desogestrel/ethinyl estradiol and ethinyl estradiol) Tablets provide two different regimens of ethinyl estradiol; 0.02 mg in the combination tablet [white] as well as 0.01 mg in the yellow tablet. Ethinyl estradiol is rapidly and almost completely absorbed. After a single dose of Mircette® combination tablet [white], the relative bioavailability of ethinyl estradiol is approximately 93% while the relative bioavailability of the 0.01 mg tablet [yellow] is 99%. The effect of food on the bioavailability of Mircette® tablets following oral administration has not been evaluated.

The pharmacokinetics of etonogestrel and ethinyl estradiol following multiple dose administration of Mircette® tablets were determined during the third cycle in 17 subjects. Plasma concentrations of etonogestrel and ethinyl estradiol reached steady-state by Day 21. The AUC_(0–24) for etonogestrel at steady-state on Day 21 was approximately 2.2 times higher than AUC_(0–24) on Day 1 of the third cycle. The pharmacokinetic parameters of etonogestrel and ethinyl estradiol during the third cycle following multiple dose administration of Mircette® tablets are summarized in Table I.

TABLE I: MEAN (SD) PHARMACOKINETIC PARAMETERS OF Mircette® OVER A 28-DAY DOSING PERIOD IN THE THIRD CYCLE (n=17).

Distribution

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