Azelastine (brand names AZEP, ASTEPRO, ASTELIN etc.) a phthalazine derivative, is an antihistamine and mast cell stabilizer available as a nasal spray for hay fever and as eye drops for allergic conjunctivitis. Azelastine is a potent antiallergic compound with histamine H1-receptor antagonist activity and a rapid onset and long duration of action. The major metabolite, desmethylazelastine, also exhibits H1- receptor antagonist activity. AZEP Nasal Spray is administered as a racemic mixture. The racemate, R- and S- enantiomers were equally potent at inhibiting eyelid histamine-induced oedema in rats, however the R-enantiomer was 2-fold less active at inhibiting eyeball histamine-induced oedema.

Azelastine (brand names AZEP, ASTEPRO, ASTELIN etc.) a phthalazine derivative, is an antihistamine and mast cell stabilizer available as a nasal spray for hay fever and as eye drops for allergic conjunctivitis. Azelastine is a potent antiallergic compound with histamine H1-receptor antagonist activity and a rapid onset and long duration of action. The major metabolite, desmethylazelastine, also exhibits H1- receptor antagonist activity. AZEP Nasal Spray is administered as a racemic mixture. The racemate, R- and S- enantiomers were equally potent at inhibiting eyelid histamine-induced oedema in rats, however the R-enantiomer was 2-fold less active at inhibiting eyeball histamine-induced oedema.