A patient with nephrogenic diabetes insipidus is started on hydrochlorothiazide, which paradoxically reduces urine output. The primary mechanism of this antidiuretic effect is:

• A Reduced GFR and enhanced proximal tubular reabsorption due to volume depletion ✓
• B Increased aquaporin-2 expression in the collecting duct
• C Stimulation of ADH release from the posterior pituitary
• D Inhibition of sodium reabsorption in the collecting duct

Explanation

Thiazides reduce urine output in nephrogenic diabetes insipidus by inducing mild volume contraction, which increases proximal tubular reabsorption of sodium and water, thereby reducing fluid delivery to the ADH-resistant collecting duct. This is a paradoxical effect since thiazides are diuretics. They do not work through ADH pathways.

Reference: Katzung Basic and Clinical Pharmacology, 15th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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