Tolvaptan is a vasopressin V2 receptor antagonist (vaptans) used in hyponatraemia and autosomal dominant polycystic kidney disease (ADPKD). Its mechanism produces:

• A Free water excretion (aquaresis) without significant natriuresis, correcting dilutional hyponatraemia ✓
• B Sodium and water excretion (saluresis) by blocking aldosterone receptors
• C Osmotic diuresis by increasing tubular osmolality
• D Increased renal water reabsorption, raising serum sodium by concentrating urine

Explanation

Tolvaptan selectively blocks V2 (vasopressin/ADH) receptors in the collecting duct principal cells, preventing cAMP-mediated insertion of aquaporin-2 water channels into the luminal membrane. This results in excretion of electrolyte-free water (aquaresis—not associated with significant sodium loss), effectively raising serum sodium concentration in dilutional or euvolaemic/hypervolaemic hyponatraemia (e.g., SIADH, heart failure, cirrhosis). In ADPKD, V2 blockade also reduces cAMP-driven cyst epithelial proliferation. Aquaresis distinguishes vaptans from conventional diuretics.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.