The CysLTs, LTC4 and LTD4, are potent mediators of asthma and hypersensitivity. They induce bronchoconstriction, increase microvascular permeability, and are vasoconstrictors of coronary arteries. Their biological effects are transduced by a pair of GPCRs, CysLT1 and CysLT2. Montelukast (sodium salt) is a potent, selective CysLT1 receptor antagonist sold under the trade name Singulair for the treatment of asthma as well as for the symptoms associated with allergic rhinitis. It binds to the human CysLT1 receptor with an IC50 of less than 5 nM with no appreciable binding to the CysLT2 receptor.