Digoxin-quinidine interaction: Changes in canine tissue concentration from steady state with quinidine

Tissue concentrations of tritiated digoxin in the dog are altered by simultaneous administration of quinidine. Serum levels rise as tissue concentration decreases significantly in all tissue except brain tissue, where an increase of 51 percent is noted over that of the control digltalized state. The digitalis toxicity associated with digoxin-quinidine interaction appears to be associated with rising brain levels of digoxin and falling levels in the myocardium. These findings suggest a neurally mediated form of toxicity with this interaction related to a change in the space of distribution. The question of possible loss of inotropic effect associated with diminished myocardial digoxin concentration requires further study.