Montelukast sodium. Molecular model of the drug montelukast sodium (C35.H36.Cl.N.Na.O3.S). This leukotriene receptor antagonist is sold under the brand name Singulair. It is used for a number of conditions including asthma, exercise induced bronchospasm, allergic rhinitis, primary dysmenorrhoea and urticaria. Atoms are represented as spheres and are colour-coded: carbon (grey), hydrogen (white), nitrogen (blue), oxygen (red), chlorine (green), sulfur (yellow) and sodium (violet).