A 62-year-old woman with heart failure who has recently started eplerenone needs monitoring for a potential electrolyte disturbance. Which parameter should be monitored most?

• A. Creatinine
• B. Potassium
• C. Liver function tests
• D. Blood pressure

Answer: (B)

Mineralocorticoid receptor antagonists like eplerenone raise the risk of hyperkalemia because they block aldosterone’s effect in the distal nephron, reducing potassium excretion. That makes serum potassium the parameter you monitor most closely when starting or adjusting this drug, especially in older patients or those with potential kidney impairment or concurrent ACE inhibitors/ARBs. While checking kidney function (creatinine) is important to gauge overall safety and dosing, the most immediate and clinically important disturbance to watch for with eplerenone is rising potassium. Liver function and blood pressure monitoring matter for other reasons, but they do not pinpoint the electrolyte disturbance this drug class most often causes.