digoxin and furosemide

Furosemide promotes renal potassium excretion, causing hypokalaemia. Reduced extracellular potassium enhances digoxin binding to the sodium-potassium ATPase pump in cardiac myocytes, increasing intracellular calcium and potentiating digoxin's effects. This pharmacodynamic interaction is amplified by furosemide-induced volume depletion and potential renal impairment, which can also raise digoxin levels.

Patients are at increased risk of digoxin toxicity, manifesting as nausea, vomiting, visual disturbances, and cardiac arrhythmias such as ventricular ectopy, atrial tachycardia with block, and severe bradycardia. Hypokalaemia is a strong independent risk factor for digoxin-induced arrhythmias, even at 'therapeutic' digoxin concentrations.

Monitor serum potassium, magnesium, renal function, and digoxin levels before and during co-administration. Correct hypokalaemia with potassium supplementation or potassium-sparing diuretics as appropriate. Adjust digoxin dose if renal function deteriorates. Advise patients to report symptoms of toxicity promptly. Consider ECG monitoring in high-risk patients.

This interaction is well established in clinical practice and supported by extensive pharmacological and clinical data. Standard cardiology and clinical pharmacology references recommend close monitoring of electrolytes when loop diuretics and digoxin are used together.