[Relative bioavailability in man of 2 pharmaceutical forms of canrenone]

The relative bioavailability of 100 mg canrenone capsules and the commercial 50 mg capsules has been determined in 12 healthy male subjects. The study was conducted in a cross over design. After the absorption phase canrenone plasma concentrations followed a biexponential decay. The half lives of the three phases observed were respectively 40.7 +/- 21.7 min, 1.94 +/- 0.558 hr and 18.5 +/- 3.93 hr after administration of a 100 mg capsules; they were respectively 31.8 +/- 14 min, 1.64 +/- 0.513 hr and 16.1 +/- 3.09 hr after administration of two 50 mg capsules. These values were similar to those reported in man. Bioequivalence of the two forms tested was ascertained by a two way analysis of variance and by the Westlake symmetrical confidence interval (95%). Peak plasma levels, Cmax, time to reach the peak, tmax, and the rate constant of absorption showed great inter and intra individual variations. In vivo hydrolysis of canrenone into canrenoic acid and subsequent lactonization of the acid are pH-dependent and could give rise to these variations if occurring before absorption.