The present invention relates to a pharmaceutical composition comprising an aqueous suspension of: (i) crystalline N-(3,4-dichlorophenyl)-3-(pyridin-4-yl)-7-oxabicyclo[2.2.1]heptane- 2-carboxamide or a pharmaceutically acceptable salt thereof; and (ii) a surfactant comprising a water-soluble co-polymer characterized by >; 5% solubility in water at 25