Source:http://linkedlifedata.com/resource/umls/id/C0771004
NCI: 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.