About Loratadine Second Generation H1 Antagonist, Antihistamine. Mechanism of Action of Loratadine Loratadine blocks one type of receptor for histamine (the H1 receptor) and thus prevents activation (activation releasing other chemicals which produce the symptoms associated with allergy) of cells by histamine. Drug also has mast cell stabilizing property. Indications for Loratadine 1. Allergic rhinitis (perennial and seasonal ) 2. Vasomotor rhinitis 3. Allergic conjunctivitis 4. Urticaria( mild, uncomplicated ) 5. Angioedema 6. Amelioration of allergic reactions to blood or plasma 7. Dermatographism 8. Adjunctive therapy in anaphylactic reactions 9. Decongestant