SBA — Single Best Answer · Review
Question 465
Pharmacology → General
Classification
Question
SSBAQuestion Header
A patient receiving a medium-efficacy diuretic develops hypokalaemia, hypochloraemic alkalosis, hyperuricaemia and hyperglycaemia. Which mechanism and nephron site best identify the drug class described?
Question Stem
Select the single best answer.
Options
A
Inhibition of the Na-K-2Cl cotransporter in the ascending limb of the loop of Henle
B
Inhibition of the Na-Cl symporter in the cortical diluting segment and early distal tubule
C
Inhibition of epithelial sodium channels with potassium conservation in the distal nephron
D
Osmotic expansion of tubular fluid by mannitol
E
Direct antagonism of beta-adrenoceptors in the juxtaglomerular apparatus
Explanation
Thiazides such as metolazone and bendroflumethiazide as medium-efficacy diuretics acting in the cortical diluting segment or early distal tubule by inhibiting the Na-Cl symporter. Their adverse effects include hypokalaemia, hypochloraemic alkalosis, hyperuricaemia and hyperglycaemia.
Option Validity
A) Na-K-2Cl cotransporter inhibition in the ascending limb characterises loop diuretics such as furosemide, bumetanide and torsemide.
C) Epithelial sodium-channel inhibition with potassium conservation describes potassium-sparing agents such as triamterene and amiloride.
D) Mannitol is an osmotic diuretic; this does not describe the thiazide mechanism or nephron site in the scenario.
E) Beta-adrenoceptor antagonism is not the mechanism by which the thiazide diuretics produce diuresis.
Further Reading
Saxena R. Textbook for MRCOG-1. Chapter 12: Pharmacology. Diuretics, pp.347–348.