The present invention relates to a canister for a metered dose inhaler (MDI). The canister comprises a high pressure chamber for containing a liquefied or compressed gas propellant and a low pressure chamber for containing an inhalable drug and vaporised propellant. The low pressure chamber has an opening for receiving a metering valve. A pressure regulating valve is interposed between the high pressure chamber and low pressure chamber and is adapted to provide a flow path from the high pressure chamber to the low pressure chamber when the pressure in the low pressure chamber drops below a predetermined pressure. The present invention also provides a metering valve for dispensing a metered dose of product from a canister containing the product and a propellant. The valve includes a metering valve body comprising a propellant metering chamber with a propellant inlet and a product metering chamber with a product inlet. It further comprises a metering valve stem with a dispensing nozzle, a propellant inlet plug and a product inlet plug. The metering valve stem is movable within the metering valve body to a dispensing position in which the propellant inlet is sealed by the propellant inlet plug and the product inlet is sealed by the product inlet plug. Furthermore, in the dispensing position, the propellant metering chamber and product metering chamber are in fluid communication with atmosphere via the dispensing nozzle of the metering valve stem such that a metered dose of product and propellant can be dispensed from the metering valve body.La présente invention concerne un flacon destiné à un inhalateur à dose mesurée (MDI). Le flacon contient une chambre à haute pression destinée à contenir un gaz propulseur liquéfié ou comprimé et une chambre à basse pression destinée à contenir un médicament inhalable et un agent propulseur vaporisé. La chambre à basse pression présente une ouverture destinée à recevoir une valve de dosage. Une valve de régulation de pression est i
