High Quality Content by WIKIPEDIA articles! Tolvaptan (INN), also known as OPC-41061, is a selective, competitive vasopressin receptor 2 antagonist used to treat hyponatremia (low blood sodium levels) associated with congestive heart failure, cirrhosis, and the syndrome of inappropriate antidiuretic hormone (SIADH). Tolvaptan was approved by the U.S. Food and Drug Administration on May 19, 2009, and is sold by Otsuka Pharmaceutical Co. under the trade name Samsca.