Which electrolyte should be monitored to prevent digoxin toxicity?

• A. Sodium
• B. Potassium
• C. Calcium
• D. Magnesium

Answer: (B)

Potassium levels are the key to preventing digoxin toxicity because digoxin inhibits the Na+/K+-ATPase pump in heart cells. When potassium is low (hypokalemia), digoxin binds more readily to that pump, amplifying its effects and raising the risk of dangerous consequences like bradycardia or heart-block. Keeping potassium in the normal range reduces digoxin binding and toxicity risk. Magnesium or calcium disturbances can affect cardiac excitability, but the most direct and actionable link for prevention is maintaining adequate potassium. In practice, monitor potassium closely in patients on digoxin, especially if diuretics or kidney issues are involved, and correct low potassium promptly to lower toxicity risk.