Particle size study of nine metered dose inhalers, and their deposition probabilities in the airways.

This study deals with the particle size measurement of nine aerosol metered dose inhalers. Calibration was made possible by the use of a laser particle velocimeter (aerodynamic Particle Sizer from TSI). The count median aerodynamic diameters (CMAD) show little variation, from 0.63 to 0.73 micron, with standard deviations (sigma g) between 1.2 and 1.8. Aerodynamic diameter aerosol diagram analysis showed multimodal mass distribution for all the tested dose inhalers. Calculations for the airway deposition probabilities (extrathoracic, tracheobronchial and alveolar) refer to the studies made by W. Stahlhofen and co-workers. As most aerosol metered dose inhalers have a predominantly bronchial therapeutic destination, the deposition at the bronchial level could be enhanced with the following parameters: inspired volume of 1500 ml, inspiratory time of 2 sec, aerosol mass median aerodynamic diameter (MMAD) of 7.5 microns, with a monodispersed distribution. The respective influences of the excipients and propellents used for the aerosolization of these dose metered inhalers are also discussed.