A 76-year-old man with heart failure and atrial fibrillation presents with blurred vision and a yellowish tint to his sight, along with fatigue and nausea; his potassium is low. Which medication is the most likely cause of this adverse drug reaction?

• A. Lisinopril
• B. Digoxin
• C. Furosemide
• D. Spironolactone

Answer: (B)

This presentation points to digoxin toxicity. Blurred vision with a yellowish tint (xanthopsia), along with fatigue and nausea, are classic neurologic and GI symptoms of digoxin overdose. The fact that potassium is low is an important clue, because digoxin binds more tightly to the Na+/K+-ATPase when extracellular potassium is limited, increasing the drug’s effects and toxicity. In a patient with heart failure and atrial fibrillation, digoxin is often used for rate control and symptom relief, but its narrow therapeutic index means that factors like hypokalemia markedly raise the risk of toxicity.

Other drugs listed don’t typically cause this triad of visual disturbance plus GI symptoms. ACE inhibitors can cause dizziness or hyperkalemia; loop diuretics like furosemide cause hypokalemia but aren’t associated with yellow vision; spironolactone causes hyperkalemia. The combination of the specific visual change and the electrolyte finding makes digoxin the best fit.