ABSTRACT
The content of this chapter addresses the laboratory assessment of aerosols emitted by orally inhaled products for aerodynamic particle size distribution (APSD). After outlining the theory of inertial particle size separation, the development of methodologies for the determination of APSD is explored, focusing primarily on those involving the pharmacopeial multi-stage cascade impactors. Abbreviated Impactor Measurement and Effective Data Analysis are two independent concepts that have been introduced for the simplification of the existing approaches, evidence for both their suitability and their limitations in product quality control is therefore examined. The widespread adoption of impactor-based methodologies has created a need for guidance on both their maintenance and system suitability verification, resulting in the development of the Good Cascade Impactor Practices concept. The tension is also explored, that currently exists between the relatively simple-in-concept apparatuses for APSD determination associated with product quality control and the more elaborate approaches that have been developed in order to make these measurements more relevant in support of the clinical program. The chapter concludes with an examination of the frequently encountered laser diffractometry and time-of flight aerodynamic particle size analysis methods. These techniques for particle size distribution are more rapid than cascade impaction and may therefore offer the prospect of more efficient early stage product development.
