Abstract: The present invention relates to the provision and use of pressurised metered dose inhalers (MDIs) for the effective administration of pharmaceutical aerosol formulations. Such formulations comprise a drug, a propellant comprising one of either 1,1,1,2-tetrafluoroethane (HFA 134a) or 1,1,1,2,3,3,3-heptafluoropropane (HFA227) or a mixture thereof, a cosolvent having a higher polarity than HFA 134a or HFA227, and a surfactant in an amount at least 0.01% by weight of said formulation. Such MDIs comprise a canister.