Medical aerosol propellants

The development of the Metered Dose Inhaler is described, with particular reference to the part played by first chlorofluorocarbons and, more recently, hydrofluorocarbons. A summary of the special propellant requirements of these medical aerosols is given, from which a clear understanding of the need for fluoroalkane propellants can be gained. An overview is given of the synthetic routes to the various propellants used, and the techniques employed to elevate a refrigerant gas to a pharmaceutical propellant. The systems and specifications used to monitor and control the quality of these gases are outlined, and an insight is given into some of the logic underpinning the regulatory control of these products.