A patient has been taking spironolactone (Aldactone) to treat heart failure. The nurse will monitor for

A. hyperkalemia: Spironolactone is a potassium-sparing diuretic that reduces sodium reabsorption while retaining potassium. This mechanism increases the risk of elevated serum potassium, which can cause cardiac arrhythmias. Regular monitoring of potassium levels is essential during therapy. B. hypoglycemia: Spironolactone does not significantly affect blood glucose, so hypoglycemia is not a typical concern. Monitoring for low blood sugar is not a primary safety measure with this medication. C. hypocalcemia: Spironolactone has minimal effect on calcium levels. Hypocalcemia is not a common adverse effect, so routine monitoring of calcium is not required for this purpose. D. hypermagnesemia: While spironolactone may slightly affect magnesium retention, significant hypermagnesemia is uncommon. Monitoring focuses primarily on potassium rather than magnesium levels.