Which electrolyte disturbance increases the risk of digoxin toxicity?

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

Answer: (A)

Potassium level modulates how strongly digoxin can bind to its target, the Na+/K+-ATPase pump in heart cells. Digoxin’s effect depends on this binding. When potassium is low (hypokalemia), there is less competition at the pump, so more digoxin binds there and its inhibitory effect increases. This amplifies the rise in intracellular calcium, boosting contractility but also raising the risk of dangerous arrhythmias and overall digoxin toxicity.

Hyperkalemia is typically a consequence of digoxin toxicity and indicates a worsening situation rather than a factor that increases risk. Hyponatremia and hypercalcemia don’t influence digoxin toxicity risk as directly or predictably as hypokalemia does. Maintaining normal potassium levels is key for patients taking digoxin to minimize toxicity risk.