Pressurized metered dose inhaler drug aerosol generation

As described in Section 3.3 in more detah, particles in the aerosol cloud should preferably have an aerodynamic diameter between 0.5 and 7.5 pm. Currently three different types of devices are used to generate aerosol clouds for inhalation nebulizers (jet or ultrasonic), (pressurized) metered dose inhalers (pMDIs) and dry powder inhalers (DPIs). The basic function of these three completely different devices is to generate a drug-containing aerosol cloud that contains the highest possible fraction of particles in the desired size range. 

Aerosols can be generated by three main drug delivery systems nebulizers, pressurized metered dose inhaler (pMDI), and dry powder inhaler (DPI). 

Inhaled respiratory therapentic agents are, as a rule, administered as aerosols. The aerosol may be an aqneons solution or suspension of the drug generated by a compressed air or ultrasonic nebulizer. Alternatively, the aerosol may be generated by a pressurized metered-dose inhaler (pMDI), a device that contains a solution or suspension of the drug in a volatile propellant such as chorofluorocarbons (CFCs)... 

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