Which electrolyte disturbance predisposes to digoxin toxicity?

• A. Hyperkalemia
• B. Hyponatremia
• C. Hypokalemia
• D. Hypocalcemia

Answer: (C)

Low potassium levels increase digoxin’s binding to its target, the Na+/K+ ATPase. Digoxin works by inhibiting this pump, which raises intracellular calcium and enhances contractility but also raises the risk of toxic effects like arrhythmias. When potassium is low, more pump sites are available for digoxin, so the drug binds more readily and toxicity is more likely. High potassium, by contrast, competes with digoxin for the same binding site and reduces its effect, making toxicity less likely. Hyponatremia and hypocalcemia don’t directly increase digoxin binding, so they’re not predisposing factors. Therefore, hypokalemia is the electrolyte disturbance that predisposes to digoxin toxicity.