Metabolism of the new antihypertensive agent pinacidil in rat, dog and man

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Abstract
The antihypertensive agent pinacidil is eliminated from the body mainly by biotransformation in the liver, followed principally by renal excretion of the metabolites. The metabolism and elimination of pinacidil is similar in rat, dog and man, and is independent of the route of administration. After an oral dose, the 24 h urinary excretion of unchanged pinacidil is 13, 4 and 5% in rat, dog and man, respectively. Fecal excretion in the rat and dog is 2 and 4%. In rat, dog and man the main biotransformation production is the pyridine-N-oxide of pinacidil. Following oral administration of pinacidil, 40, 54 and 54%, respectively, is excreted in the urine as the N-oxide during the 1st 24 h, and less than 1% in the feces in rat and dog. Three unidentified minor metabolites were found in plasma, urine and feces in rat and dog. The major metabolite, the pyridine-N-oxide of pinacidil, has an anti-hypertensive potency .apprx.1/4 of that of pinacidil. In animals and human volunteers with normal kidney function, the plasma conentration of the N-oxide are always lower than those of the parent compound, so that the metabolite contributes little to the antihypertensive effect of pinacidil.