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Question 445
Pharmacology → General
Classification
Question
SSBAQuestion Header
Two patients receive different diuretics. Drug X is a high-ceiling diuretic acting in the ascending limb of the loop of Henle. Drug Y is a medium-efficacy diuretic acting mainly in the cortical diluting segment or early distal tubule. Which transporter pairing is correct?
Question Stem
Select the single best answer.
Options
A
Drug X inhibits Na-Cl symport; Drug Y inhibits Na-K-2Cl cotransport
B
Drug X inhibits an epithelial sodium channel; Drug Y inhibits Na-K-2Cl cotransport
C
Drug X inhibits Na-K-2Cl cotransport; Drug Y inhibits Na-Cl symport
D
Drug X antagonises aldosterone; Drug Y inhibits an epithelial sodium channel
E
Drug X inhibits Na-Cl symport; Drug Y antagonises aldosterone
Explanation
Loop diuretics such as furosemide, bumetanide and torsemide are high-ceiling agents acting in the ascending limb of the loop of Henle by inhibiting Na-K-2Cl cotransport. Thiazide diuretics such as metolazone and bendroflumethiazide are medium-efficacy agents acting primarily in the cortical diluting segment or early distal tubule by inhibiting the Na-Cl symport.
Option Validity
A) This reverses the transporter targets of loop and thiazide diuretics.
B) Epithelial sodium-channel inhibition is associated with potassium-sparing agents such as triamterene and amiloride, not high-ceiling loop diuretics.
D) Aldosterone antagonism and epithelial sodium-channel inhibition describe potassium-sparing mechanisms rather than the loop/thiazide pair in the stem.
E) Neither transporter assignment matches the high-ceiling loop diuretic described as Drug X.
Further Reading
Saxena R. Textbook for MRCOG-1. Chapter 12: Pharmacology. Diuretics, pp.347–348.