Comparative pharmacokinetics of nicardipine hydrochloride, a new vasodilator, in various species.

1. The pharmacokinetics of a new potent vasodilator, 2-(N-benzyl-N-methylamino)-ethyl methyl 2,6-dimethyl-4-(m-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylate hydrochloride (nicardipine hydrochloride), were studied after oral and i.v. dosage to rats, dogs, monkeys and humans. 2. The plasma half-life and volume of distribution in humans after i.v. administration did not change with dosage in clinical range. In rats and dogs these parameters increased with higher doses, probably because of the potent vasodilative effect of the drug. 3. The plasma clearance in dogs and humans was not affected by dosage, but in rats tended to increase slightly with higher doses. 4. Systemic availability after oral administration was low in spite of excellent absorption, indicating a marked first-pass effect. Increased systemic availability with increased dose indicates that the metabolic activity of the liver may become partly saturated with the drug or its metabolites. 5. Disappearance of the drug from the plasma after i.v. administration was fastest in rats > dogs approximately monkeys > humans. The terminal half-life of the drug after i.v. administration to humans was about 1 h.