Objective To outline the role of a new drug, tolvaptan, in treating severe and chronic hyponatraemia. Tolvaptan decreases aquaporin expression in renal collecting ducts, by inhibiting antidiuretic hormone (ADH)-V2 receptors, to promote free water clearance. Given its mechanism of action, this drug seems the ideal treatment for the syndrome of inappropriate antidiuretic hormone secretion (SIADH) when the osmotic imbalance leads to life threatening complications.

Data sources A case is described of severe hyponatraemia deriving from SIADH secondary to meningoencephalitis in a patient admitted to hospital for traumatic brain injury.

Data extraction Clinical, laboratory and radiological data at presentation and for a 1 year of follow-up were analysed.

Data synthesis Tolvaptan ameliorated hyponatraemia, brain oedema and consciousness, and drug withdrawal led to recurrence of hyponatraemia and coma.

Conclusions In patients with SIADH, which is not self-limited, and is associated with severe cognitive impairment, the use Tolvaptan may prove life saving and should be rigorously evaluated.