ABSTRACT
Propellant-driven, or pressurized, metered dose inhalers (pMDIs) have now been used for pharmaceutical inhalation aerosols for 50 years. Their introduction, in 1956, was revolutionary in that they allowed the development of formulations for repeated, reproducible dose delivery through a metering valve for airway administration (1). Significant changes to pMDIs have transpired with the phaseout of ozone depleting propellants based on chlorofluorocarbon (CFC) chemistry but pMDIs, especially those based on hydrofluoroalkane (HFA) chemistry, remain an important component of inhalation aerosol delivery systems.
