Standardized entrainment tubes for the evaluation of pharmaceutical dry powder dispersion

A series of standardized entrainment tubes (SETs) were designed to provide a method for evaluation of aerosol dispersion of pharmaceutical powders. The range of specific resistances (RD) provided by the SETs encompassed those of commercial DPIs. The airflow conditions within the SETs were characterized in terms of pressure drop (ΔP), power, Reynoldʹs number (Re) and shear stress (τs) at airflow rates of 28.3 and 60 L/min. The aerosol performance of a commercial powder formulation (Ventolin Rotacaps™) obtained using the SETs was measured by cascade impaction; and characterized using emitted dose (ED), fine particle mass (FPM), mass median aerodynamic diameter (MMAD) and geometric standard deviation (GSD). The use of SETs allowed the aerosol performance of the powder formulation to be measured under well defined geometry and flow conditions. Good reproducibility in ED, FPM and MMAD results were obtained from SETs. Comparable values were obtained from SETs at similar resistance levels to the commercial inhaler devices (Rotahaler™ and Inhalator™). The SETs enabled examination of fundamental relationships between airflow conditions and aerosol performance.