Pharmacokinetics of Spironolactone After a Single Dose: Evaluation of the true Canrenone Serum Concentrations During 24 Hours

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Abstract
In humans spironolactone is metabolized to a large number of metabolites (including canrenone), which are measured by fluorometry. The serum levels of canrenone and other fluorogenic metabolites have been determined by fluorometry in 8 healthy volunteers after administration of a single dose of spironolactone 100 mg. True canrenone levels were measured by a specific HPLC assay. The mean Cmax of true canrenone was only 33% of the Cmax of canrenone + other metabolites. The fraction of true canrenone rises during 24 hours, indicating that canrenone has a slower elimination rate than the other metabolites. The mean of the ratios of the AUC (0-24h) determined by HPLC and the fluoro-metrically determined AUC was 46%. From the literature it is known, that the pharmacological potency of canrenone is only about 1/3 of an equivalent amount of all spironolactone metabolites. From this, combined with our present results, it can