All of the following statements about amiloride are true EXCEPT:
**Core Concept**
Amiloride is a potassium-sparing diuretic that acts by blocking the epithelial sodium channel (ENaC) in the collecting duct of the kidneys, leading to increased sodium excretion and reduced potassium excretion. This results in increased water excretion and increased blood volume.
**Why the Correct Answer is Right**
Amiloride works by competitively inhibiting the sodium ion entry into the principal cells of the collecting duct, which in turn reduces sodium reabsorption and increases sodium excretion. This action is independent of aldosterone and is mediated through the ENaC. By blocking ENaC, amiloride prevents the sodium ions from entering the cells, which reduces the amount of sodium that is reabsorbed into the bloodstream.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because amiloride is not a loop diuretic; it is a potassium-sparing diuretic that acts on the collecting duct, not the loop of Henle.
**Option B:** Incorrect because amiloride does not work by inhibiting the Na+/K+ ATPase pump; it works by blocking the ENaC.
**Option C:** Incorrect because amiloride does not have a significant effect on the renin-angiotensin-aldosterone system (RAAS); its action is independent of aldosterone.
**Clinical Pearl / High-Yield Fact**
One notable side effect of amiloride is its potential to cause hyperkalemia, particularly when used in combination with other potassium-sparing diuretics or in patients with renal impairment. This is because amiloride reduces potassium excretion, leading to increased potassium levels in the blood.
**Correct Answer: B. Amiloride works by inhibiting the Na+/K+ ATPase pump.**