The present invention is directed to dihydrogen phosphate salt 2-(3-{6-[2-(2,4-dichloro-phenyl)-ethylamino]-2-methoxy-pyrimidin-4-yl}-ph- enyl)-2-methyl-propionic acid of Formula (III), a pharmaceutical composition comprising a pharmaceutically effective amount of the compound of Formula (III), and a pharmaceutically acceptable carrier; and a method of treating a patient suffering from a PGD2-mediated disorder including, but not limited to, allergic disease (such as allergic rhinitis, allergic conjunctivitis, atopic dermatitis, bronchial asthma and food allergy), systemic mastocytosis, disorders accompanied by systemic mast cell activation, anaphylaxis shock, bronchoconstriction, bronchitis, urticaria, eczema, diseases accompanied by itch (such as atopic dermatitis and urticaria), diseases (such as cataract, retinal detachment, inflammation, infection and sleeping disorders) which is generated secondarily as a result of behavior accompanied by itch (such as scratching and beating), inflammation, chronic obstructive pulmonary diseases, ischemic reperfusion injury, cerebrovascular accident, chronic rheumatoid arthritis, pleurisy, ulcerative colitis and the like, by administering to said patient a pharmaceutically effective amount of the compound of Formula (III).