Inhaled therapies have existed for at least 5000 years (1). Modern drug therapy can be traced to the propellant-driven (also known as "pressurized") metered-dose inhaler (pMDI) of the 1950s (2). The surge in interest that has arisen in the last decade relates to the chlorofluorocarbon (CFC) propellant ban and the development of biotechnology products. The observation that CFC propellants play a significant role in ozone depletion in the upper atmosphere (3), which in turn results in greater surface ultraviolet (UV) radiation and impact on public health, particularly the incidence of skin cancer, led to regulation in the late 1980s (4). In addition, the burgeoning biotechnology industry of the late 1980s and early 1990s actively sought alternative methods of delivering macro-molecular drugs, which were difficult to deliver in therapeutic doses by the oral or parenteral route (5). The urgent need for alternative methods explains the diversity of devices that have been described in the patent literature, many of which are currently on the market, and the others are under development.
The factors governing lung deposition may be divided into those related to the physicochemical properties of the droplets or particles being delivered, the mechanical aspects of aerosol dispersion usually associated with the delivery device, and the physiological and anatomical considerations associated with the biology of the lungs.
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