A pharmaceutical formulation comprising a substantially clear aqueous solution having a viscosity of less than 10 mPa.s containing 3.5 to 5% w/v of 1,3-bis(2-carboxychromon-5-yloxy)-propan-2-ol, or a pharmaceutically acceptable salt thereof, as active ingredient and glycerol, the concentration of ions of metals of groups IIA, IB, IIB and IVB of the periodic table or of transition metals being less than 20 ppm.