Which medication interaction increases the risk of digoxin toxicity by causing potassium depletion?

• A. Spironolactone
• B. Furosemide
• C. Hydrochlorothiazide
• D. Hydralazine

Answer: (B)

Potassium level is a key factor in how digoxin affects the heart. Digoxin inhibits the Na+/K+-ATPase pump; when potassium is low, there are fewer competing K+ ions, so more digoxin binds to the pump and its effects are amplified. Loop diuretics like furosemide cause significant potassium loss, leading to hypokalemia and thus increase the risk of digoxin toxicity. Spironolactone, a potassium-sparing diuretic, tends to keep potassium higher, which can help mitigate this risk. Hydralazine doesn’t alter potassium, and while hydrochlorothiazide can cause potassium loss, the strongest interaction with digoxin toxicity comes from the pronounced potassium depletion seen with loop diuretics. In practice, monitor potassium closely in patients on digoxin who are also taking loop diuretics to reduce the risk of toxic effects.