Comparative antiarrhythmic activity of quinidine combined with propranolol and with sotalol

Quinidine combined with propranolol produces antiarrhythmic synergism. The mechanism is uncertain but has been suggested as possibly due to increased activity of quinidine made possible by myocardial beta adrenergic receptor blockade by propranolol. In the present study, identical doses of quinidine were coadministered with doses of propranolol and of sotalol that produced equivalent beta blockade. Antiarrhythmic activity was measured as decreased ventricular vulnerability to electrical fibrillation in the dog and prevention of chloroform-induced ventricular fibrillation in the mouse. The two drug combinations did not produce equivalent antiarrhythmic activity because only quinidine-propranolol produced antiarrhythmic synergism.