Azelastine (CAS: 58581-89-8) is a selective H1-receptor antagonist and mast cell stabilizer with the chemical formula C₂₂H₂₄ClN₃O and molecular weight 381.90 g/mol. It appears as a white to off-white powder. As a pharmaceutical intermediate and active ingredient, it is primarily used as an antihistamine to treat allergic conditions. It is commonly applied in nasal sprays to relieve symptoms of seasonal and perennial allergic rhinitis, such as sneezing, runny nose, and nasal congestion. Additionally, it is used in eye drops to manage allergic conjunctivitis, reducing itching, redness, and swelling in the eyes. Its anti-inflammatory properties make it effective in controlling allergic reactions and providing long-lasting relief. Azelastine is also sometimes prescribed for managing symptoms of non-allergic rhinitis and can be used topically for urticaria to alleviate itching and rashes. It works by inhibiting the release of histamine and other mediators from mast cells.