Interactions between digoxin and potassium-sparing diuretics.

A kinetic and hemodynamic study of digoxin was performed in six healthy subjects and similar studies were performed during digoxin with spironolactone and with triamterene. Spironolactone reduced renal tubular secretion of digoxin and attenuated its positive inotropic effect (evaluated by systolic time intervals and echocardiography) and triamterene reduced the extrarenal elimination of digoxin, but induced no changes in digoxin-elicited inotrophy. It is suggested that the renal handling of digoxin is influenced by the intracellular potassium concentration in the renal tubular cell. The results indicate a drug-receptor interaction between spironolactone metabolites and digoxin at the hypothetical inotropic digitalis receptor. Amiloride has been reported to suppress digoxin inotropism, whereas spironolactone induces minor inhibition and triamterene does not affect digoxin inotropism.