To evaluate and compare the effects of first generation anti-histamine (chlorpheniramine maleate) and second generation anti-histamine (loratadine) on isolated trachea of rabbit.

Objective: The incidence of respiratory allergy has increased gradually over the past several years and current estimates suggest that allergic rhinitis affects approximately 20% of the population. Large scales population surveys indicate that up to 38% of patients with rhinitis have asthma. The allergic response in the airways is an important pathogensis to cause bronchoconstriction owing to increased responsiveness of tracheo bronchial tree to various stimuli and also causes the release of histamine and other chemical mediators from mast cells.