The nurse is caring for a patient who is taking hydrochlorothiazide (HydroDIURIL) and digoxin (Lanoxin). Which potential electrolyte imbalance will the nurse monitor for in this patient?

A. Hypernatremia: Hydrochlorothiazide promotes sodium excretion, so high sodium levels are unlikely. The medication tends to lower sodium, making hypernatremia an uncommon concern in this combination therapy. B. Hypokalemia: Hydrochlorothiazide increases renal potassium excretion, which can lower serum potassium levels. Low potassium enhances the risk of digoxin toxicity, including arrhythmias, making close monitoring essential. This electrolyte imbalance is the most significant concern with this drug combination. C. Hypocalcemia: Thiazide diuretics like hydrochlorothiazide actually decrease calcium excretion, so low calcium levels are not expected. Monitoring calcium is not a primary concern for this patient. D. Hypermagnesemia: Hydrochlorothiazide increases magnesium excretion, but high magnesium levels are unlikely. Hypermagnesemia is not a common side effect of this therapy and is not a priority for monitoring in this scenario.