The US subsidiary of Japan's Astellas Pharma says it has received approval from the Food and Drug Administration for an additional indication for its drug Vaprisol which is used to treat a life-threatening condition that occurs when the body's blood sodium level falls significantly below normal.

The agency has given the go-ahead to Vaprisol (conivaptan), which was first approved in December 2005 to treat euvolemic hyponatremia, which occurs when the body retains water but not sodium, for the related condition of hypervolemic hyponatremia, in which the body retains water and sodium, but more of the former.

Vaprisol is an arginine vasopressin antagonist, and induces water loss without depleting sodium and other electrolytes, unlike diuretic drugs, and Astellas noted that it is the world's first drug specifically approved to treat hyponatremia, which is estimated to affect up to 4% of hospitalised patients in the USA each year.

Common causes of the condition include advanced kidney failure, cancer, hypothyroidism and chronic high blood pressure. Although many patients with hyponatremia show no symptoms, in severe cases, it may result in swelling of the brain, respiratory arrest and death.

Yoshihiko Hatanaka, chief executive at Astellas Pharma US, said that this additional indication, Vaprisol “will provide physicians with an important new treatment option for patients with this often serious condition.” The company has previously said that the drug has the potential to become a $100 million-a-year product.