The invention concerns an aerosol solution composition intended for use with a pressurised metered dose inhaler, comprising glycopyrronium bromide and formoterol, or a salt thereof, optionally in combination with one or more additional active ingredient, stabilised by a selected amount of a mineral acid and wherein the amount of the degradation product N-(3 -bromo)- [2-hydroxy-5-[1-hydroxy-2-[1-(4- methoxyphenyl)propan-2-ylamino] ethyl] phenyl] formamide is lower than the limit of quantification, when stored in accelerated conditions at 25°C and 60% relative humidity (RH) for at least 3 months in an aerosol can provided with a metering valve having at least a butyl rubber gasket. The optional one or more active ingredient may be an inhalation corticosteroid selected from beclometasone dipropionate, budesonide or its 22R-epimer, ciclesonide, flunisolide, fluticasone propionate, fluticasone furoate, mometasone furoate, etc.
