Pharmacology · Class

Vasopressin receptor antagonists (vaptans) !

Medicines that block the antidiuretic hormone receptor in the kidney: they remove free water and raise low blood sodium.

Updated 2026-11-01

What they are

Antagonists of vasopressin (antidiuretic hormone) receptors. Tolvaptan, by mouth, is selective for the renal V2 receptor; conivaptan, IV, blocks V1a and V2. They treat hypervolaemic or euvolaemic hyponatraemia (heart failure, SIADH), and tolvaptan also slows kidney growth in polycystic kidney disease.

Mechanism of action

Vasopressin acting on V2 receptors of the collecting duct inserts aquaporin-2 water channels into the cell membrane. Blocking V2 keeps those channels out, so free water is lost in dilute urine (aquaresis) while sodium is mostly kept, and serum sodium rises.

Target: Vasopressin V2 receptor (and V1a for conivaptan)

Drugs in this class

TolvaptanAn oral V2 receptor blocker that removes free water and raises low sodium in heart failure and SIADH. Started in…Vasopressin V2 receptor

Others in the class

Conivaptan
Lixivaptan

Test yourself

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What is aquaresis?

The loss of free water in dilute urine without much loss of sodium, caused by blocking the V2 receptor and its aquaporin-2 channels.

Why are vaptans started in hospital?

Serum sodium can rise too fast; overly rapid correction of chronic hyponatraemia can cause osmotic demyelination.

In which type of hyponatraemia are vaptans contraindicated?

Hypovolaemic hyponatraemia, where the problem is volume loss and fluids are needed.

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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: DailyMed - TOLVAPTAN tablet (DailyMed (U.S. National Library of Medicine), 2026); Tolvaptan (low blood sodium): MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2018); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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