Azelastine hydrochloride is a potent, second-generation, selective, histamine antagonist.Target: Histamine ReceptorAzelastine hydrochloride is a selective H(1)-receptor antagonist that inhibits histamine release and interferes with activation of several other mediators of allergic inflammation. Azelastine hydrochloride can inhibit CHMCs activation and release of IL-6, tryptase, and histamine. On an equimolar basis, azelastine was a more potent inhibitor than olopatadine [1]. 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 [2]. 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 [3].

References:
[1]. Kempuraj, D., et al., Azelastine is more potent than olopatadine n inhibiting interleukin-6 and tryptase release from human umbilical cord blood-derived cultured mast cells. Ann Allergy Asthma Immunol, 2002. 88(5): p. 501-6.
[2]. Canonica, G.W., et al., Topical azelastine in perennial allergic conjunctivitis. Curr Med Res Opin, 2003. 19(4): p. 321-9.
[3]. Lieberman, P., M.A. Kaliner, and W.J. Wheeler, Open-label evaluation of azelastine nasal spray in patients with seasonal allergic rhinitis and nonallergic vasomotor rhinitis. Curr Med Res Opin, 2005. 21(4): p. 611-8.