Stable pharmaceutical solution formulations for pressurized metered dose inhalers

The invention relates to stable pharmaceutical solution to be used with pressurised metered dose inhalers (MDIs) suitable for aerosol administration. In particular, the invention relates to solution to be used with pressurised metered dose inhalers (MDIs), suitable for aerosol administration containing -agonists and stable at room temperature for a pharmaceutically acceptable shelf-life. An aerosol solution composition for use in an aerosol inhaler comprises an active material, a propellant containing a hydrofluoroalkane, a cosolvent and optionally a low volatility component to increase the mass median aerodynamic diameter (MMAD) of the aerosol particles on actuation of the inhaler. The composition is stabilized by using a small amount of mineral acid and a suitable can having part or all of its internal metallic surfaces made of stainless steel, anodized aluminium or lined with an inert organic coating.