The effect of nifedipine on serum digoxin concentrations in patients.

Drug interactions with digoxin are being increasingly recognized. Some calcium antagonists have been shown to alter digoxin kinetics and changes in digoxin dosage have been recommended. To determine whether nifedipine affects serum digoxin concentrations in patients during combined drug administration, serum digoxin concentrations were determined before and during concomitant drug administration in 14 cardiac patients. The mean (+/- SD) digoxin concentration was 0.92 +/- 0.5 ng/ml before and 0.96 +/- 0.5 ng/ml after 4 days of nifedipine therapy in eight inpatients. For the group of 14 patients, the mean level was 0.78 +/- 0.4 ng/ml before nifedipine and 0.8 +/- 0.4 ng/ml after 1 week of combined drug administration, and 0.84 +/- 0.5 ng/ml after 2 weeks of combined drug administration. These data suggest that nifedipine does not significantly alter serum digoxin concentrations in cardiac patients receiving combined digoxin and nifedipine in the clinical setting.