Mozavaptan hydrochloride (OPC-31260 hydrochloride) is a benzazepine derivative and a potent, selective, competitive and orally active vasopressin V 2 receptor antagonist with an IC 50 of 14 nM. Mozavaptan hydrochloride shows ~85-fold selectivity for V 2 receptor over V 1 receptor (IC 50 of 1.2 μM), and can antagonize the antidiuretic action of arginine vasopressin (AVP) in vivo. Mozavaptan hydrochloride has the potential for hyponatremia, syndrome of inappropriate antidiuretic hormone (SIADH), and congestive heart failure treatment .