Effects of nifedipine and diltiazem on plasma levels and renal excretion of beta-acetyldigoxin

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Abstract
The possible effects of nifedipine and diltiazem on digoxin kinetics by measuring glycoside plasma concentrations and renal excretion before and during dosing in 23 patients with cardiac insufficiency achieving steady-state conditions. Mean (.+-. SD) digoxin plasma concentration was 0.64 .+-. 0.22 before and 0.61 .+-. 0.21 ng/ml during nifedipine dosing in 11 subjects over a period of 10-14 days. Renal digoxin clearance was not influenced by nifedipine, whereas total body clearance and extrarenal clearance of digoxin increased slightly. Diltiazem resulted in a 24-70% (.hivin.X = 46%) increase in plasma digoxin concentrations in 8 of 12 subjects. Renal digoxin clearance was not influenced by diltiazem, whereas total body clearance and extrarenal clearance of digoxin were reduced 28 and 44% in 5 of the 8 subjects in whom renal digoxin excretion was measured. Nifedipine has no significant effects on digoxin kinetics, but digoxin plasma concentrations should be controlled in subjects receiving digoxin with diltiazem until new steady-state digoxin concentrations are established, and the digoxin dose should be reduced if there is evidence of toxicity.