A client is taking digoxin. Which lab value is most important to check regularly?

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

Answer: (B)

Potassium level is the most important lab to monitor regularly with digoxin because potassium and the digoxin-affected Na+/K+-ATPase pump directly interact. Digoxin increases intracellular calcium to boost heart contraction, but its effect depends on how much the pump is blocked, which in turn depends on potassium competing for the same site. When potassium is low, more digoxin can bind to the pump, increasing the risk of toxicity and dangerous heart rhythms. Keeping potassium in the normal range reduces the chance of digoxin toxicity while the drug does its job. While kidney function (creatinine) is also important for dosing and clearance, the electrolyte status—especially potassium—has the most immediate impact on safety.