Which medication increases the patient’s risk of Digoxin toxicity by promoting potassium loss?

• A. Furosemide
• B. Metformin
• C. Nitroglycerin
• D. Coumadin

Answer: (A)

The key idea is that low potassium levels increase the risk of digoxin toxicity. Loop diuretics like furosemide promote potassium loss in the distal tubule, which can lead to hypokalemia. Digoxin works by inhibiting the Na+/K+ ATPase pump in cardiac cells; when potassium is low, digoxin binds more readily to this pump, amplifying its effects. That heightened inhibition causes more calcium to accumulate inside heart cells, which can trigger dangerous arrhythmias and other toxicity symptoms.

So a medication that causes potassium wasting directly raises the chance of digoxin toxicity, making furosemide the correct choice. The other drugs listed don’t promote potassium loss or directly increase digoxin toxicity through this mechanism. Metformin, nitroglycerin, and warfarin do not affect potassium or the digoxin–pump interaction in the way loop diuretics do.