Tolvaptan is an ADH receptor antagonist. It can be used as an alternative or possible addition to water restriction or sodium chloride administration in patients with hyponatremia. Cost for the drug generally prohibits this from being used as a first line agent.
Tolvaptan should NOT be used in hyponatremic patients who are volume depleted in whom volume repletion with saline is the primary treatment.
Source
Rose, B. "Overview of the treatment of hyponatremia" Up to Date. 16 Oct 2009.