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Chapter 15: Diuretics & Other Drugs That Act on the Kidney

A 70-year-old retired businessman with a history of chronic heart failure has been taking digoxin and furosemide. He is now admitted with a history of vomiting, acute decompensated heart failure, and metabolic derangements. He has marked peripheral edema and metabolic alkalosis (pH, 7.50; pCO2, 45; HCO3, 36; Na+, 140). Which of the following drugs is most appropriate for the treatment of his edema?

(A) Acetazolamide

(B) Digoxin

(C) Eplerenone

(D) Hydrochlorothiazide

(E) Tolvaptan

Although acetazolamide is rarely used in heart failure, carbonic anhydrase inhibitors are quite valuable in patients with edema and metabolic alkalosis. The high bicarbonate levels in these patients make them particularly susceptible to the action of carbonic anhydrase inhibitors. Digoxin is useful in chronic systolic failure but is not first-line therapy and may cause vomiting, with depletion of stomach acid and reduced serum chloride; increasing the digoxin dose might cause arrhythmias. Tolvaptan might be useful if the patient were hyponatremic. Hydrochlorothiazide and eplerenone are not adequate for first-line therapy of edema in acute heart failure. The answer is A.

A 50-year-old man has a history of frequent episodes of renal colic with calcium-containing renal stones. A careful workup indicates that he has a defect in proximal tubular calcium reabsorption, which results in high concentrations of calcium salts in the tubular urine. The most useful diuretic agent in the treatment of recurrent calcium stones is

(A) Chlorthalidone

(B) Diazoxide

(C) Ethacrynic acid

(D) Mannitol

(E) Spironolactone

The thiazides are useful in the prevention of calcium stones because these drugs reduce tubular calcium concentration, probably by increasing passive proximal tubular and distal convoluted tubule reabsorption of calcium. In contrast, the loop agents (choice C) facilitate calcium excretion. Diazoxide is a thiazide-like vasodilator drug but has no diuretic action; in fact, it may cause sodium retention. It is used in hypertension and insulinoma (see Chapter 11). The answer is A.

Which of the following is an important effect of chronic therapy with loop diuretics?

(A) Decreased urinary excretion of calcium

(B) Elevation of blood pressure

(C) Elevation of pulmonary vascular pressure

(D) Metabolic alkalosis

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