Plasma protein binding of nilvadipine, a new dihydropyridine calcium antagonist, in man and dog.

The in vitro protein binding of nilvadipine, a new dihydropyridine calcium antagonist, was studied by equilibrium dialysis, ultracentrifugation, and equilibrium gel filtration. In the experiment with equilibrium dialysis, nilvadipine was highly bound to the plasma of man (97.5-98.7%) and dog (99.1-99.2%) with no plasma concentration dependency in a range of 10-100 ng/ml. Ultracentrifugation gave lower protein binding than that by equilibrium dialysis. From the experiments with equilibrium dialysis and equilibrium gel filtration, we found that lipoproteins and albumin are the main nilvadipine binding proteins in the plasma. The protein binding of nilvadipine in human plasma was unaffected or slightly decreased in the presence of therapeutic concentration of phenytoin, diazepam, salicylic acid, propranolol, quinidine and trichloromethiazide.