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Mifepristone |
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CLINICAL PHARMACOLOGY Pharmacodynamic Activity The anti-progestational activity of mifepristone results from competitive interaction with progesterone at progesterone-receptor sites. Based on studies with various oral doses in several animal species (mouse, rat, rabbit and monkey), the compound inhibits the activity of endogenous or exogenous progesterone. The termination of pregnancy results. Pharmacokinetics and Metabolism Absorption Following oral administration of a single dose of 200 mg, mifepristone is rapidly absorbed, with a peak plasma concentration of 1.98 mg/l occurring approximately 90 minutes after ingestion. The absolute bioavailability of a 20 mg oral dose is 69%. Distribution Mifepristone is 98% bound to plasma proteins, albumin and α1-acid glycoprotein. Binding to the latter protein is saturable, and the drug displays nonlinear kinetics with respect to plasma concentration and clearance. Following a distribution phase, elimination of mifepristone is slow at first (50% eliminated between 12 and 72 hours) and then becomes more rapid with a terminal elimination half-life of 18 hours. Excretion By 11 days after a 200 mg dose of compound, 83% of the drug has been accounted for by the feces and 9% by the urine. Serum levels are undetectable by 11 days. Special Populations The effects of age, hepatic disease and renal disease on the safety, efficacy and pharmacokinetics of mifepristone have not been investigated.
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