Pranlukast (ONO-1078) is a potent, selective and orally active CysLT1 receptor antagonist. Sold under the trade name Ultair, it was the first cysteinyl (peptidyl) leukotriene receptor antagonist (LTRA) marketed for the treatment of asthma. Clinical studies in Japan, Europe, and North America all show that pranlukast significantly attenuates bronchoconstriction in response to a variety of allergen challenges as well as to inhaled LTD4. Pranlukast binds to the human CysLT1 and CysLT2 receptors with IC50 values of approximately 4-7 nM and 3,600 nM, respectively.