Effects of flow pattern, device and formulation on particle size distribution of nebulized aerosol.

The evaluation of particle size recommended in the pharmacopeias requires a constant flow rate, and the method for pediatric inhaled drugs is the same as for adult drugs. In this study, the aerosol concentration and particle size distribution (PSD) were measured under a realistic breathing pattern and constant flow. Two types of nebulizer (i.e., breath-enhanced nebulizer and vibrating-mesh nebulizer) and two formulations (i.e., budesonide suspension and albuterol solution) were chosen for comparison. The aerosol concentration under the realistic pattern was not constant, which was different from the result at constant flow. The changing trend of aerosol concentration varied with the operation process of each device. The aerosol concentration profile was similar between budesonide suspension and albuterol solution. As to the PSD, as inspiratory flow increased, the X50 (50% undersize) increased with all nebulizers but Omron microAir NE-U22 nebulizer. There was good agreement between X50 obtained under the realistic inhalation patterns and their equivalent average flow rates by Bland-Altman analysis, although the X50 obtained under the realistic inhalation pattern was greater than value at constant flow. The agreement of the two breath-enhanced jet nebulizers was better than that of the vibrating-mesh nebulizers. The X50 of budesonide was not equal to that of albuterol when using the same nebulizer. Interestingly, a significant difference was observed in the X50 and Span when comparing the results of PSD under adult and child breathing patterns. Furthermore, all vibrating-mesh nebulizers produced aerosol droplets having larger mean diameter and narrower size distribution than those of the air-jet nebulizers. We conclude that it will be more conducive to the evaluation of particle size to use a laser diffractometer under a realistic pattern and make up for the shortcomings of cascade impactors. The effects of flow pattern, nebulizer and formulation should be taken into account in the evaluation of the qualities of nebulizer products in pharmaceutical practice.