Tolvaptan: a new therapeutic agent.

Tolvaptan is a new agent in the treatment of normovolemic and hypervolemic hyponatremia. It is a V(2) receptor antagonist inducing free water diuresis. It has been recently approved in USA and Europe for the treatment of hyponatremia associated with SIADH, cirrhosis as well as heart failure, while in hypovolemic hyponatremia its use is contraindicated. The drug also appears to be effective in the acute exacerbations of heart failure that need hospitalization. In the short-term tolvaptan seems to relieve acute congestive symptoms and improves mortality. However, the long-term effects on mortality are still controversial. The favorable short-term effects are ascribed to the selective V(2) receptor blocking, while the unopposed stimulation of V(1A) may give an explanation for the lack of long-term benefit. The drug should be initiated in the hospital setting because careful monitoring of fluid balance is recommended. It is administered orally giving the advantage of continuation in the outpatient setting. Moreover tolvaptan may have a role in the treatment of autosomal dominant polycystic kidney disease (ADPKD). Its effectiveness has been shown in animal models and Phase 3 clinical trial as well as an open-label study is now active. Since tolvaptan is metabolized by the cytochrome CYP3A4 in the liver physicians should be aware of possible drug to drug interactions. Resulting from large studies tolvaptan appears well tolerated. Common side effects are thirst, dry mouth and polyuria. Tolvaptan opens a new page not only in the treatment of normovolemic and hypervolemic hyponatremia but also in the treatment of acute decompensated heart failure and probably in ADPKD.