Selective cysteinyl leukotriene receptor 1 (CysLT1) antagonist (IC50 values are ~ 4 - 7 and 3620 nM for CysLT1 and CysLT2 respectively). Inhibits contraction of airway smooth muscle, microvascular leakage into airways and eosinophil infiltration. Can decrease symptoms of bronchial asthma.