Saturday December 26, 2009
About Tolvaptan (Samsca)

Tolvaptan (Samsca) is the first oral dosage form in a class known as “selective vasopressin antagonists.” These drugs, also referred to as “vaptans,” cause renal elimination of water without increasing urinary excretion of sodium or potassium. An injectable vaptan, conivaptan (Vaprisol), has been available in the U.S. since 2006. Both conivaptan and tolvaptan are indicated for the treatment of hyponatremia. In addition, tolvaptan has been studied for treating heart failure.

Once-daily Samsca has been shown to significantly raise serum sodium concentrations in as early as 8 hours, and the change was maintained for 30 days. Exposure and response to Samsca are similar in patients with a creatinine clearance of 10-79 mL/min and in patients without renal impairment; thus no dosage adjustment is necessary.

The unique mechanism of action of Samsca selectively blocks the binding of vasopressin to the V2-receptors in the collecting duct of the kidney. If the V2-receptors are left unblocked, the binding of vasopressin with these receptors can cause water retention resulting in hyponatremia. By inhibiting the effects of vasopressin at the V2-receptor, Samsca increases the excretion of free water, while the excretion of sodium and other electrolytes is not directly affected (aquaresis).