### 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%. Azurette (desogestrel and ethinyl estradiol tablets, USP and ethinyl estradiol tablets, USP) provide two different regimens of ethinyl estradiol; 0.02 mg in the combination tablet [dark blue] as well as 0.01 mg in the green tablet. Ethinyl estradiol is rapidly and almost completely absorbed. After a single dose of desogestrel/ethinyl estradiol combination tablet [dark blue], the relative bioavailability of ethinyl estradiol is approximately 93% while the relative bioavailability of the 0.01 mg tablet [green] is 99%. The effect of food on the bioavailability of Azurette tablets following oral administration has not been evaluated.

The pharmacokinetics of etonogestrel and ethinyl estradiol following multiple dose administration of desogestrel/ethinyl estradiol and ethinyl estradiol 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 desogestrel/ethinyl estradiol and ethinyl estradiol tablets are summarized in Table I.

### Distribution

Etonogestrel, the active metabolite of desogestrel, was found to be 99% protein bound, primarily to sex hormone-binding globulin (SHBG). Ethinyl estradiol is approximately 98.3% bound, mainly to plasma albumin. Ethinyl estradiol does not bind to SHBG, but induces SHBG synthesis. Desogestrel, in combination with ethinyl estradiol, does not counteract the estrogen-induced increase in SHBG, resulting in lower serum levels of free testosterone.96–99

### Metabolism

Desogestrel: Desogestrel is rapidly and completely metabolized by hydroxylation in the intestinal mucosa and on first pass through the liver to etonogestrel. Other metabolites (i.e., 3α-OH-desogestrel, 3β-OH-desogestrel, and 3α-OH-5α-H-desogestrel) with no pharmacologic actions also have been identified and these metabolites may undergo glucuronide and sulfate conjugation.

Ethinyl estradiol: Ethinyl estradiol is subject to a significant degree of presystemic conjugation (phase II metabolism). Ethinyl estradiol escaping gut wall conjugation undergoes phase I metabolism and hepatic conjugation (phase II metabolism). Major phase I metabolites are 2-OH-ethinyl estradiol and 2-methoxy-ethinyl estradiol. Sulfate and glucuronide conjugates of both ethinyl estradiol and phase I metabolites, which are excreted in bile, can undergo enterohepatic circulation.

### Excretion

Etonogestrel and ethinyl estradiol are excreted in urine, bile, and feces. At steady state, on Day 21, the elimination half-life of etonogestrel is 27.8±7.2 hours and the elimination half-life of ethinyl estradiol for the combination tablet is 23.9±25.5 hours. For the 0.01 mg ethinyl estradiol tablet [green], the elimination half-life at steady state, Day 28, is 18.9±8.3 hours.