Review Question - QID 212563

This patient with signs of congestive heart failure as well as muscle cramping and weakness most likely has hypokalemia due to chronic thiazide use. The new channel blocker diuretic that also compensates for hypokalemia is therefore most likely amiloride.

Amiloride and triamterene are epithelial sodium channel blockers (ENaC) that work on the collecting duct of the nephron. Since this channel is responsible for the bulk of sodium absorption in this segment, these diuretics can lead to synergistic sodium excretion when used in combination with other diuretics. Furthermore, in the collecting duct, the absorption of sodium leads to a luminal negative charge that results in potassium or proton excretion. Therefore, use of these channel blockers will also result in potassium and proton sparing.

Incorrect Answers:
Answer 1: Acetazolamide is a carbonic anhydrase inhibitor that acts primarily on the proximal tubule; however, it would not be used in this situation nor would it correct potassium defects.

Answer 3: Furosemide is a loop diuretic that acts primarily on the thick ascending limb of the loop of Henle; however, this diuretic would worsen hypokalemia because it is a potassium wasting diuretic.

Answer 4: Hydrochlorothiazide is a loop diuretic that acts primarily on the distal convoluted tubule; however, this diuretic would worsen hypokalemia because it is a potassium wasting diuretic.

Answer 5: Spironolactone is a competitive aldosterone receptor antagonist that acts primarily in the collecting tubule; it would have the same effects as amiloride; however, the mechanism of action is not blocking a channel.

Bullet Summary:
Amiloride and triamterene block the epithelial sodium channel in the collecting duct of the nephron.