The Effect of Quinidine and Other Oral Antiarrhythmic Drugs on Serum Digoxin

Abstract

We compared the effects of quinidine and three alternate antiarrhythmic drugs on serum digoxin concentration in 63 patients before and during administration of quinidine, procainamide, disopyramide, or mexiletine. Quinidine increased digoxin concentration by at least 0.5 nmol/L in 21 of 22 patients: Mean serum digoxin rose from 1.2 nmol/L to 2.4 nmol/L (P < 0.001). Procainamide, disopyramide, or mexiletine increased serum digoxin by 0.5 nmol/L in one of 41 patients. Anorexia, nausea, and vomiting developed soon after starting quinidine therapy in 10 of the 22 patients who received quinidine but in only five of the 41 patients who received procainamide, disopyramide, or mexiletine (P < 0.01). Quinidine prolonged the PR interval from 160 ± 14 ms to 183 ± 26 ms, but procainamide, disopyramide, and mexiletine did not change the PR interval (P < 0.005). In digitalized patients, quinidine increases serum digoxin concentration, increases digoxin's effect on atrioventricular conduction, and produces more adverse gastrointestinal effects than procainamide, disopyramide, or mexiletine.