The Delivered Dose Uniformity (DDU) and Aerodynamic Particle Size Distribution (APSD) are two of the main Critical Quality Attributes (CQAs) in measuring the therapeutic efficacy of orally inhaled and nasal products.
The data produced by both of these tests can be severely compromised if the flow rate used during testing is inaccurate and/or inconsistent.
Indeed, Stokes’ Law which describes the relationship between stage cut-off diameter, nozzle diameter and air flow rate, demonstrates that a 5% deviation in flow rate changes the stage cut-off diameter by approximately 2.5%.
At a flow rate of 60 L/min for example, Stage 1 of an Andersen Cascade Impactor should give a theoretical cut-off of 4.4 microns – increase that rate to 63 L/min and cut-off is effectively decreased to 4.3 microns.
Copley Scientific offers two Flow Meters with the required range and accuracy to measure the flow in inhaler testing systems, one based on differential pressure and the other on thermal mass measurement methods.
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