Plume Geometry: examination of processing schemes and inter-analyst variability…We Can Do Better!
Christopher J Gruenloh, Karen M Schmidt, Jenna C Caragiulo and Karina S McKinney
PPD, Part of Thermo Fisher Scientific, 8556 Research Way, Middleton, WI 53562, USA
Summary
Spray pattern (SP) and plume geometry (PG) are spray characterization techniques used during the development of pressurized metered-dose inhalers (pMDIs) and nasal sprays. SP is employed for routine quality control testing and both tests are required to evaluate test and innovator products in the generic approval pathway. PG is generally thought to not accurately reflect the performance of either device or formulation and is perceived as variable and subjective. One also needs to recognize as well as reconcile differences in the performance of SP and PG testing with a time-averaged image submitted for processing the former whereas a single “snapshot” image is typically used for the latter. While today’s SP test has become much less subjective through use of images captured by high-speed cameras with laser light illumination and automated software processing routines, questions and perceptions remain for PG, where the analyst must select the frame processed, the spray angle origin and the placement of “arms” to indicate the outer limits of the plume. The objective of this study was to examine the repeatability of PG measurements across a series of 4 commercially available pMDI products with 3 analysts processing. Using the same data sets, the impacts of time-averaging vs. snapshot images as well as different techniques to define the origin and outer edges of the plume were investigated. Data indicates that both inter-analyst and product variability in PG processing can be greatly reduced through use of a time-averaged image with an intensity-based methodology to define the plume’s outer edges.