Comparison of impaction and non-impaction methods for measuring spray patterns from MDIs

Z. Pitluk, S. Pallas, J. Graaf, D. Farina

This paper presents a comparison of impaction and non-impaction spray pattern methods as recommended by the U.S. FDA in a recently published draft guidance describing in vitro tests for establishing bioequivalence (BE) of test and reference metered dose inhalers (MDIs) containing albuterol sulfate [1]. The spray pattern results for both methods were collected at 3 cm from the MDI actuator mouthpiece edge from albuterol sulfate MDI product samples using an automated actuation system with parameters derived from a previously conducted QbD-based usage study of trained testers within the product’s targeted patient population as recommended by the U.S. FDA [2]. The impaction and non-impaction measurements were collected using a fax paper method and the Proveris SprayVIEW® NMDI instrument respectively. Results include: 1) comparisons of spray pattern Dmin, Dmax, and Ovality (ratio of Dmax to Dmin) measurements for each method; 2) spray pattern area measurements for the non-impaction method according to FDA recommendations [1],[2]; and 3) high-speed laser illuminated videos of the aerosol plume impacting the fax paper surface. Qualitative images and the ovality ratio results confirmed that the methods produced similarly shaped spray patterns. However, the impaction method results showed significantly more variability, with smaller reported Dmin and Dmax values, than the non-impaction results. The high-speed laser illuminated videos showed a significant amount of particle bounce from the fax paper surface and the clear formation of the normally “free-jet” plume transforming into a “wall-jet” plume due to the surface’s presence – both consistent with the smaller reported spray pattern results

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