• Publication Date: 04/01/2024
  • Author(s):
    Mitchell, Jolyon P. Roberts, Daryl L.
  • Organization(s):
    Applied Particle Principles, LLC Jolyon Mitchell Inhaler Consulting Services, Inc.
  • Article Type: Technical Articles
  • Subjects: Instruments, Particle Characterization, Product Development/Formulation, Testing, Validation, and Regulatory Compliance

Oddly missing from the pharmacopeial compendia and archival literature are flow resistance data for glass microfiber filters common to the delivered dose uniformity (DDU) testing protocols described in the USP and European Pharmacopeias. The authors undertook a laboratory investigation to provide insight into how filter flow resistance can vary across several similar products available commercially. They also discuss ways this variability can be handled in practice by users of inhaler testing methods.

The authors found surprisingly large variations in resistance for ostensibly similar filter types, based on their labeling. Because this information is absent from the technical specifications and brochures for these filter products, they recommend that users determine filter resistance for themselves, using a simple test system. They believe that filter flow resistance variability is a far more significant parameter that should not be neglected as a source of data variability. Consequently, they urge industrial users to generate and publish more data so that these characteristics of the typical pharmacopeial test equipment can move towards standardization.

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