Antihistaminics are effective in relieving histamine related symptoms like sneezing, itching and rhinorrhea but least effective in reversing nasal obstruction which is due to other mediators. They are first line treatment for mild allergic rhinitis or pollen induced disease.
First generation antihistaminics like chlorphenamine, promethazine cross blood brain barrier and result in somnolence, cognitive impairment, dryness of mouth and paradoxical reaction like restlessness, rarely seizure. Newer generation antihistaminics like cetirizine, loratidine, and fexofenadine do not cross blood brain barrier and are more specific action on peripheral H1 receptors. Intra nasal antihistaminics, azelastine, levocabastine and Olopatadine are as effective as oral antihistaminics but are indicated in children above 6 yearsof age.
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