Montelukast (trade name Singulair)(Openair in Pakistan) is a leukotriene receptor antagonist (LTRA) used for the maintenance treatment of asthma and to relieve symptoms of seasonal allergies.[1] It is usually administered orally. Montelukast is a CysLT1 antagonist; that is it blocks the action of leukotriene D4 on the cysteinyl leukotriene receptor CysLT1 in the lungs and bronchial tubes by binding to it.