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Pharm Dev Technol. 1996 Oct;1(3):261-8.

Comparison of a respiratory suspension aerosolized by an air-jet and an ultrasonic nebulizer.

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University of Maryland, Department of Pharmaceutical Sciences, Baltimore 21201, USA.


In the absence of USP standards and performance monographs, this research sought to determine if differences in the aerosolization mechanism (air-jet vs. ultrasonic) affected droplet and insoluble particle deposition of a nebulized model respiratory suspension. Five milliliters of a model suspension containing 0.1% w/v fluorescein (to estimate droplet deposition) and known quantities of 1, 3, and 6 microns latex spheres (representing insoluble drug particles) was aerosolized from an air-jet and an ultrasonic nebulizer. Nebulized output was collected in a modified Andersen impactor. Samples were analyzed spectrophotometrically (490.5 nm) and by a Coulter Counter to estimate droplet and sphere deposition, respectively. The distribution of droplets throughout the modified impactor for both nebulizers suggested that both the air-jet and the ultrasonic nebulizer produced droplets (0.4 to 10 microns in aerodynamic diameter) large enough to incorporate 1, 3, and 6 microns insoluble spheres. However, Coulter Counter analysis of the sphere distribution revealed that while the air-jet nebulized output contained spheres of all sizes, this was not true for the ultrasonic nebulizer. In the ultrasonic nebulizer, 99% of the spheres (irrespective of size) were not aerosolized and were recovered from the nebulizer reservoir at the aerosolization end point. The results highlight the importance of evaluating performance of a respiratory suspension in combination with a specific nebulizer. When conducting in vitro inertial deposition testing of a respiratory suspension, it is inappropriate to assume that deposition trends of droplets will predict the deposition of the insoluble dispersed phase.

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