Which medicine is most likely to cause hyperkalemia?

• A. Metformin
• B. Lisinopril
• C. Spironolactone
• D. Furosemide

Answer: (C)

Potassium balance is mainly managed by aldosterone, which promotes potassium excretion in the kidney. A drug that blocks aldosterone’s action in the collecting ducts reduces potassium loss, leading to hyperkalemia. Spironolactone is a potassium-sparing diuretic that antagonizes the mineralocorticoid receptor, so it directly decreases potassium excretion and increases its retention. This makes hyperkalemia a common risk, especially in patients with kidney impairment or on other potassium-raising medications.

Metformin doesn’t affect potassium levels. Lisinopril can raise potassium by lowering aldosterone, but spironolactone’s mechanism is more directly and potently potassium-sparing. Furosemide, a loop diuretic, tends to cause potassium loss (hypokalemia) rather than retention.