Vasopressin-receptor antagonists-vaptans for short-suppress the action of the hormone arginine vasopressin (AVP), which plays a key role in sodium and water balance. Increased AVP levels can trigger free water reabsorption in the kidneys, which may lead to increased blood volume and hyponatremia.

Vaptans are categorized into various subclasses and can be taken orally or I.V.

* Conivaptan (Vaprisol) has been FDA-approved to treat euvolemic and hypervolemic hyponatremia in hospitalized patients. Hyponatremia is the most common electrolyte imbalance in hospitalized patients. Conivaptan is contraindicated in patients with hypovolemic hyponatremia.

* Relcovaptan shows promise for treating painful menstruation, Reynaud's disease, and preterm labor.

* Mozavaptan, lixivaptan, satavaptan, and tolvaptan can remove excess water from the body without disturbing electrolyte balance, an advantage over diuretics.

* Other vaptans are being studied to treat diabetic nephropathy, cirrhosis, depression, glaucoma, Mnire's disease, cerebral vasospasm in subarachnoid hemorrhage, and small cell lung cancer.

Source: Decaux G, et al., Non-peptide arginine-vasopressin antagonists: The vaptans, The Lancet, May 10, 2008.