<p>Montelukast is a selective and orally active leukotriene receptor antagonist that inhibits the cysteinyl leukotriene receptor (CysLT1). The cysteinyl leukotrienes (LTC4, LTD4, LTE4) are products of arachidonic acid metabolism and are released from various cells, including mast cells and eosinophils. Cysteinyl leukotrienes and leukotriene receptor occupation have been correlated with the pathophysiology of asthma &amp; allergic rhinitis, including airway edema, smooth muscle contraction, and altered cellular activity associated with the inflammatory process, which contribute to the signs and symptoms of asthma.</p>