[Studies of biological availability. A critical assessment based on a study of spironolactone preparations].

Investigations have been performed to determine the relative bioavailability of canrenone from an improved spironolactone preparation, Deverol drgs., in comparison with canrenone from a spironolactone standard preparation on the Austrian market (Osiren drgs.). This was carried out by comparing the areas under the serumconcentration-time-curves under conditions of steady-state after oral application of both preparations. Additionally the contents of spironolactone in the two preparations tested were determined. By intraindividual comparison of the areas under the serum-concentration-time-curves of canrenone a relative bioavailability of 99.37% of canrenone from Deverol drgs. could be calculated versus canrenone from the standard. However a remarkable different content of spironolactone in the preparations was found: in 50 mg of Deverol drgs. 50.5 mg spironolactone and in 100 mg of Osiren drgs. 109.6 mg spironolactone were found. Determination of drug contents in products appears to be necessary to determine their relative bioavailability correctly, because the usual range of +/- 5% may be overshot as demonstrated in our investigation.