Which statement best explains why digoxin toxicity occurred in the elderly patient described?

• A. Electrolyte disturbances increasing digoxin binding to Na+/K+ ATPase
• B. Decreased renal clearance of digoxin
• C. Increased P-glycoprotein efflux of digoxin
• D. Direct myocardial toxicity of digoxin at normal levels

Answer: (A)

The key idea is how electrolyte balance alters how strongly digoxin can affect the heart. In older adults, electrolyte disturbances—especially low potassium from diuretics—make the Na+/K+-ATPase pump bind digoxin more avidly. When this pump is inhibited more by digoxin, intracellular calcium rises, which increases contractility but also disrupts electrical conduction and promotes dangerous arrhythmias. So, even if the digoxin level isn’t dramatically high, the heightened sensitivity from low potassium drives toxicity. Reduced renal clearance can raise levels, but the most direct reason the elderly patient developed toxicity is the electrolyte-related increase in digoxin’s binding and effect on the pump.