Otsuka Pharmaceutical Co., Ltd. announces that the oral vasopressin V₂-receptor antagonists Samsca^® Tablets, Samsca^® OD Tablets and SAMSCA^® Granules 1% have received regulatory approval in Japan for the indication of hyponatraemia secondary to the syndrome of inappropriate antidiuretic hormone secretion (SIADH) in adults.

Samsca (generic name is tolvaptan) is a novel compound discovered by Otsuka designed as an orally available antagonist of the vasopressin V₂receptor. It inhibits water reabsorption at the renal collecting duct, thereby enhancing water diuresis (aquaresis) without depletion of electrolytes.

SIADH is a disease state in which vasopressin is inappropriately released beyond the physiological regulatory mechanism, due to various underlying diseases (e.g. vasopressin producing tumors, central nervous system, pulmonary diseases). Inappropriately secreted vasopressin causes water retention by increasing water reabsorption, resulting in dilutional hyponatremia.

Tolvaptan was approved in the US in 2009 for the treatment of clinically significant hypervolemic and euvolemic hyponatremia, including patients with heart failure and SIADH, and in the European Union (EU) in 2009 for the treatment of hyponatremia secondary to SIADH in adults.