Both Montair LC and Allegra-M are anti-allergic medicines used for the management of symptoms of allergic rhinitis. There is a difference in their composition. Montair LC contains a combination of Montelukast and Levocetirizine while Allegra-M contains a combination of Montelukast and Fexofenadine. Your doctor will decide which one to prescribe to you after accessing your disease condition.