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

1. The antihypertensive agent pinacidil is eliminated from the body mainly by biotransformation in the liver, followed principally by renal excretion of the metabolites. 2. The metabolism and elimination of pinacidil is similar in rat, dog and man, and is independent of the route of administration. 3. After an oral dose, the 24 h urinary excretion of unchanged pinacidil is 13, 4, and 5% in rat, dog and man, respectively. Faecal excretion in the rat and dog is 2 and 4%. 4. In rat, dog and man the main biotransformation product 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 first 24 h, and less than 1% in the faeces in rat and dog. 5. Three unidentified minor metabolites were found in plasma, urine and faeces in rat and dog. 6. The major metabolite, the pyridine-N-oxide of pinacidil, has an anti-hypertensive potency about a quarter of that of pinacidil. In animals and human volunteers with normal kidney function, however, the plasma concn. 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.