Amrinone metabolism

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Abstract
Amrinone (Inocor, 5-amino-3,4''-bipyridin-6(1H)-one) is an inotropic drug. High performance liquid chromatographic methods for the analysis of amrinone in plasma, and for both amrinone and its N-acetyl metabolite in urine were developed and applied to measure specimens obtained from a number of healthy men who had received i.v. or oral amrinone. The i.v. doses ranged from 0.8-2.2 mg/kg. Terminal elimination of amrinone from the bloodstream followed apparent-1st-order kinetics. Half-life (t1/2), after the drug had distributed to the tissues, was estimated by a log-linear least-squares regression; mean t1/2 was 2.6 .+-. 1.4 h. During the first 24 h after medication, unchanged amrinone excreted in the urine of these subjects represented 10-40% of the dose. N-Acetyl metabolite in the urine represented < 2% of the dose. In the oral study, doses ranged from 25-250 mg (0.31-3.5 mg/kg) and the maximum plasma concentration attained was proportional to the dose. The 1st order terminal elimination t1/2 was possibly dose-related. In only 1 subject were there unequivocal amounts of the N-acetyl metabolite in the plasma.