A new diuretic is being studied in human volunteers. Compared with placebo, the new drug increases urine volume, decreases urinary Ca2+, increases body pH, and decreases serum K+. If this new drug has a similar mechanism of action to an established diuretic, it probably
**Core Concept**
The new diuretic's mechanism of action is likely related to its effects on electrolyte balance and acid-base status. This involves the inhibition of sodium reabsorption in the kidneys, leading to increased sodium excretion and water loss.
**Why the Correct Answer is Right**
The new diuretic's effects on increasing urine volume, decreasing urinary Ca2+, increasing body pH, and decreasing serum K+ are characteristic of loop diuretics, which act by inhibiting the Na-K-2Cl cotransporter in the thick ascending limb of the loop of Henle. This leads to increased sodium and chloride delivery to the distal tubules, resulting in increased potassium excretion and metabolic alkalosis. The decreased urinary Ca2+ is due to the increased calcium reabsorption in the proximal tubules secondary to the increased sodium reabsorption.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because thiazide diuretics, which inhibit the Na-Cl cotransporter in the distal convoluted tubule, typically increase urinary Ca2+ and can cause hypokalemia but do not usually cause metabolic alkalosis.
**Option B:** This option is incorrect because osmotic diuretics, such as mannitol, increase urine volume by drawing water into the tubules but do not typically cause significant changes in serum potassium or acid-base status.
**Option C:** This option is incorrect because aldosterone antagonists, such as spironolactone, can cause hyperkalemia and metabolic acidosis, which is opposite to the effects seen with the new diuretic.
**Option D:** This option is incorrect because carbonic anhydrase inhibitors, such as acetazolamide, can cause metabolic acidosis and do not typically cause significant changes in serum potassium.
**Clinical Pearl / High-Yield Fact**
When using loop diuretics, it is essential to monitor serum potassium levels and consider potassium-sparing diuretics or potassium supplements to prevent hypokalemia.
**Correct Answer:** C.