The FDA has approved Samsca tablets (tolvaptan) to treat hyponatremia, one of the most common electrolyte disorders seen in hospitalized patients. Hypnoatremia is associated with heart failure, cirrhosis, and the syndrome of inappropriate antidiuretic hormone.

According to the drug’s manufacturer, Otsuka Pharmaceutical Co., Ltd., in Tokyo,  Samsca is the only oral selective vasopressin antagonist available for treating hyponatremia. Samsca raises and maintains serum sodium concentrations by increasing the excretion of free water (aquaresis) without directly affecting the excretion of sodium or impacting kidney function.

In the Study of Ascending Levels of Tolvaptan in Hyponatremia 1 and 2 clinical trials, 424 patients with euvolemic or hypervolemic hyponatremia (serum sodium less than 135 mEq/L) were treated for 30 days with Samsca or placebo, then followed for an additional seven days after cessation.

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As soon as eight hours after the first dose, patients using the drug experienced an increase in sodium levels greater than those seen with placebo. Samsca should be initiated only in a hospital, where patients’ serum sodium can be monitored closely, as too rapid a rise in sodium can cause osmotic demyelination syndrome.