This editorial looks at vasopressin 2 receptor antagonists (e.g tolvaptan), which promote the excretion of water without loss of electrolytes, for the treatment of hyponatraemia. 

Tolvaptan has recently been licensed in the UK for the treatment of hyponatraemia secondary to the syndrome of inappropriate antidiuretic hormone secretion (SIADH).  The author summarises the data this was based upon and notes that the license is more restricted than the US, where it is approved for use in hyponatraemia secondary to congestive heart failure and liver cirrhosis.  They discuss possible safety issues with vasopressin 2 receptor antagonists, for example they may have detrimental effects in hypovolaemic hyponatraemia, because they can aggravate existing hypovolaemia as a result of increased clearance of free water.

The author comments that the role of these agents remains unclear; evidence for long-term benefit is lacking and there are few data on morbidity and mortality (“for £74.68 a day, more evidence of benefit is needed”).  They say that fluid restriction remains the main treatment for managing the SIADH; “as no trials or cost-benefit analyses have compared fluid restriction, demeclocycline, and vasopressin receptor antagonists, there is no evidence that these new drugs are any better than the much cheaper standard treatment.”