Which medication can cause hyperkalemia by decreasing renal potassium excretion?

• A. Potassium sparing diuretic (Spironolactone)
• B. Furosemide
• C. Thiazide diuretics
• D. ACE inhibitors

Answer: (A)

Potassium balance in the kidney is governed by aldosterone acting in the collecting ducts, which normally promotes potassium secretion into the urine. A potassium-sparing diuretic blocks aldosterone’s action, so the collecting duct reabsorbs sodium with less potassium being secreted into the tubular fluid. This reduces renal potassium excretion and allows potassium to accumulate in the blood, leading to hyperkalemia. Spironolactone, a potassium-sparing diuretic that antagonizes the aldosterone receptor, exemplifies this mechanism. In contrast, loop and thiazide diuretics increase potassium loss in the urine, causing hypokalemia; ACE inhibitors can also raise potassium but by lowering aldosterone production rather than directly decreasing potassium excretion in the distal nephron. Thus, the medication most likely to cause hyperkalemia through decreased renal potassium excretion is a potassium-sparing diuretic like spironolactone.