Quinidine-digoxin interaction (author's transl)

Abstract

An additional dose of 500 mg of rapidly absorbed quinidine increased the digoxin concentration in serum after 3-5 hours by up to 46% and prolonged digoxin half life from 50 to 100 hours in six probands who were on chronic quinidine-digoxin medication. These effects were not elicited regularly in persons pretreated with digoxin only. The results show that quinidine both diminishes elimination and produces transient redistribution of digoxin. Chronic quinidine medication leads to protracted digoxin elimination resulting in marked prolongation of digoxin half life. This is the reason for persisting increase of digoxin concentration in serum. Estimation of serum digoxin levels should thus be done 8 hours after the last quinidine (and digoxin) medication at the earliest. On cessation of digoxin, as is done preparing for electric cardioversion, one should remember that digoxin elimination is clearly prolonged should quinidine treatment be continued.