Pharmacology: Pharmacokinetics: Spironolactone is fairly rapidly absorbed from the gastrointestinal tract, the extent of absorption depending on particle size and formulation. Modern formulations are reported to provide bioavailability of about 90%. It is about 90% bound to plasma proteins. Spironolactone is metabolized extensively to a number of metabolites including canrenone and the sulfur-containing 7-thiomethyl spironolactone, both of which are pharmacologically active. The major metabolite may be 7-thiomethyl spironolactone, although it is uncertain to what extent the actions of spironolactone are dependent on the parent compound or its metabolites. Spironolactone is excreted mainly in the urine and also in feces, in the form of metabolites. Spironolactone or its metabolites may cross the placental barrier, and canrenone is distributed into breast milk.
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