Digoxin-quinidine interaction in patients with chronic renal failure

We evaluated the effect of quinidine on digoxin pharmacokinetics in six patients with severe renal failure. Quinidine reduced the total body clearance of digoxin from 1.87 to 1.06 l/hour (p < 0.001), and prolonged the digoxin half-life of elimination from 5.20 to 9.61 days (p < 0.01). The digoxin volume of distribution was unchanged. Renal clearance of digoxin was negligible; thus, the decrease in total body clearance was due to a decrease in the nonrenal clearance of digoxin. The mean trough serum concentrations of quinidine ranged from 1.0 to 3.0 μg/ml. We conclude that in patients with chronic renal failure, the dose of digoxin should be decreased by 50% if quinidine therapy is initiated.