NCIt definition : The hydrochloride salt form of azelastine, a phthalazinone derivative with antihistaminergic
activity. Azelastine hydrochloride competes with histamine for the H1 receptor, thereby
diminishing the actions of histamine on effector cells and decreasing the histamine-mediated
symptoms of allergic reaction, such as bronchoconstriction, vasodilation, increased
capillary permeability and spasmodic contractions of gastrointestinal smooth muscle.;