Reduction of digoxin-induced inotropism during quinidine administration.

A kinetic and dynamic study of digoxin was performed in 6 healthy subjects, and repeated in the same subjects after administration of quinidine for 1 wk. Myocardial performance evaluated by systolic time intervals increased in parallel with plasma digoxin concentration, whereas left ventricular end-diastolic diameter on echocardiography and arterial blood pressure remained constant. The positive inotropic effect of digoxin was abolished during concomitant treatment with quinidine. Quinidine has been reported to increase the risk of digitoxicity, and therefore the treatment with digoxin and quinidine in combination should be reconsidered.