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Absorption
Mean bioavailability is 65% (range, 26% to 170%). C max at steady state is 4.9 to 13.7 ng/mL (mean, 9.2 ng/mL) ( Propecia ). C max is 37 ng/mL (range, 27 to 49 ng/mL) ( Proscar ). T max is 1 to 2 h. AUC 0-24 is 20 to 154 ng•h/mL (mean, 53 ng•h/mL).
Distribution
Vd ss is 44 to 96 L (mean, 76 L) and is about 90% bound to plasma proteins. The drug crosses the blood-brain barrier but does not appear to distribute preferentially to the CSF.
Metabolism
Extensively metabolized in the liver, primarily via the CYP-450 3A4 enzyme subfamily. Two metabolites have been identified: t-butyl side chain monohydroxylated and monocarboxylic acid; each possesses no more than 20% activity.
Elimination
Plasma Cl is 70 to 279 mL/min (mean, 165 mL/min). Mean t ½ is 4.8 h (range, 3.3 to 13.4 h) ( Propecia ). Mean t ½ is 6 h (range, 3 to 16 h) ( Proscar ); 32% to 46% is excreted in the urine as metabolites, and 51% to 64% is excreted in the feces.
Special Populations
Elderly
Mean t½ increases to 8 h (70 yr of age and older). Mean AUC 0-24 increases 15%.
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