Azelastine is a potent, second-generation, selective, histamine antagonist.Target: Histamine ReceptorAzelastine is a selective H(1)-receptor antagonist that inhibits histamine release and interferes with activation of several other mediators of allergic inflammation. Azelastine can inhibit CHMCs activation and release of IL-6, tryptase, and histamine. On an equimolar basis, azelastine was a more potent inhibitor than olopatadine. Topical azelastine progressively improved itching and conjunctival redness in PAC patients compared to placebo and was at least as effective as levocabastine. Rapid relief is consistent with H(1)-receptor antagonist action, while continued improvement up to 6 weeks may be consistent with mechanisms involving other mediators of allergic inflammation . Azelastine nasal spray was reported to control all rhinitis symptoms, including nasal congestion, regardless of rhinitis diagnosis during the 2-week study period. Patients with seasonal allergic rhinitis and patients with seasonal allergic rhinitis plus nonallergic triggers were identified as patient types most likely to respond to azelastine nasal spray .