Diltiazem,: An average increase in steady state plasma digoxin concentration of 22% was observed when diltiazem, 180 mg/day, was given to 24 normal subjects who were receiving l3-acetyldigoxin, 0.2 mg daily . There is minimal pharmacokinetic interaction between diltiazem and digoxin . The magnitude of the diltiazem interaction is small; therefore, digoxin dose adjustment is probably unnecessary

Nifedipine : There is no pharmacokinetic interaction between nifedipine and digoxin, either in patients or in normal subjects .

Tiapamil, a congener of verapamil, causes an increase in serum digoxin levels of 60%, similar to that of verapamil .

– Interaction With Diuretic Drugs

Furosemide and sodium-induced diuresis one of the mechanisms responsible for the increase in digoxin clearance due to sodium loading was diminished passive proximal back diffusion of filtered and secreted digoxin. reported that diuresis caused a 70% increase in digoxin clearance and a 20% decrease in serum digoxin levels in 10 patients who were taking digoxin for atrial fibrillation and who did not have congestive heart failure. Mechanisms that have been identified for renal excretion of digoxin include glomerular filtration, tubular secretion and proximal tubular reabsorption of digoxin. When the sodium diet was liberalized to a moderately high sodium diet, the digoxin clearance increased by 70% and the serum digoxin levels decreased by 20%.

Diuresis-induced hypokalemia It is well known that hypokalemia is associated with sensitivity to digitalis and, thus, increases its toxicity , but it is not well appreciated that when the serum potassium is as low as 2 to 3 mEq/liter, the tubular secretion of digoxin is nearly blocked. Although thiazides and loop diuretic drugs themselves do not alter the kinetics of digoxin excretion, they induce a dose-dependent loss of potassium from the body, resulting in a decreased serum potassium concentration.