Montelukast Sodium(Singulair) is a potent, selective, anti-inflammatory CysLT1 receptor antagonist (IC50 < 5nM) with no appreciable affect on the CysLT2 receptor. In rat colitis Montelukast Sodium (Singulair) has demonstrated the ability to increase PGE2 production and lower COX-2 expression. Inhibition is competitive with respect to leukotrienes - particularly LTD4, a biologically active mediator that plays an important role in the control of several biochemical pathways involving pulmonary and immune system function.