Pharmacology: Pharmacokinetics: Cyproterone acetate is slowly absorbed from the gastrointestinal tract with peak plasma concentration being achieved in three or four hours. It is about 96% bound to plasma proteins. The terminal elimination half-life is about 38 hours. Cyproterone is metabolized in the liver; about 35% of a dose is excreted in urine as free and conjugated metabolites, the remainder being excreted in the bile. The principal metabolite 15β-hydroxycyproterone, has anti-androgenic activity.
Ethinylestradiol is absorbed well and rapidly by the gastrointestinal tract. The presence of an ethinyl group at the 17-position greatly reduces hepatic first-pass metabolism compared with estradiol, enabling the compound to be much more active if taken orally. There is some initial conjugation at the gut wall, and the systemic bioavailability is only 40%. Ethinylestradiol is highly protein bound, unlike naturally occurring estrogens, which are mainly bound to sex hormone-binding globulin; it is principally bound to albumin. It is metabolized in the liver, and excreted in urine and feces. Metabolites undergo enterohepatic recycling.