Review Question - QID 101017

The patient in this scenario was given furosemide to decrease excess fluid retention in congestive heart failure (CHF). Furosemide decreases calcium and magnesium absorption in the thick ascending loop of Henle.

Furosemide inhibits the Na+/K+/2Cl- cotransport system in the thick ascending loop of Henle. Both calcium and magnesium are reabsorbed paracellularly in the thick ascending loop of Henle because the luminal contents are electrically positive relative to the blood. Because furosemide decreases the electric potential in the lumen, reabsorption of calcium and magnesium is decreased, and serum levels of both ions fall.

Chavey et al. discuss the management of systolic heart failure. Over 5 million adults suffer from systolic heart failure. Diuretics, including furosemide, are used to manage and remove excess fluid in states of volume overload.

Atsmon et al. discuss drug-induced hypomagnesemia. Cisplatin, amphotericin B, cyclosporin, and other medications may cause significant hypomagnesemia and thus warrant routine magnesium monitoring. The diuretics furosemide and hydrochlorothiazide have a less severe hypomagnesemic effect and do not require routine monitoring of magnesium levels.

Illustration A shows the site of action of several diuretics. Note that the loop diuretics, furosemide, ethacrynic acid, and bumetanide, act on the thick ascending loop of Henle.

Incorrect Answers:
Answer 1: Acetazolamide and mannitol act on the proximal tubule. Acetazolamide may cause metabolic acidosis, while mannitol may cause pulmonary edema and/or hypovolemia.
Answer 2: The descending loop of Henle is not a common site of diuretic action.
Answer 4: The thiazide group of diuretics act at the distal tubule. While the drugs cause hypomagnesemia, they can be differentiated from loop diuretics because they cause HYPERcalcemia.
Answer 5: The potassium-sparing diuretics act at the cortical collecting duct. These drugs can cause hyperkalemia. Spironolactone can cause gynecomastia.