A study by the European Pharmaceutical Aerosol Group (EPAG) titled “Effect of Sampling Volume on Dry Powder Inhaler (DPI)-Emitted Aerosol Aerodynamic Particle Size Distributions (APSDs) Measured by the Next-Generation Pharmaceutical Impactor (NGI) and the Andersen Eight-Stage Cascade Impactor (ACI)” and published on June 8, 2012 by AAPS PharmSciTech finds that reduced volume cascade impaction of DPIs will require further investigation.
The authors, Hlack Mohammed of GSK, Daryl Roberts of MSP Corporation, Mark Copley of Copley Scientific, Mark Hammond of Melbourn Scientific, Steven Nichols of OINDP Consultancy, and Jolyon Mitchell of Trudell Medical, investigated the possibility of using lower volumes than the 4.0 L currently specified by the US and European pharmacopoeias for aerodynamic particle size distribution analysis using the NGI and ACI. The internal volume of the ACI eight-stage impactor is 1.155 L, and the internal volume of the NGI is 2.025 L.
According to EPAG, “many stakeholders would like to see [the required volume] reduced to a lower volume in an attempt to match the volumes typically inhaled, as this may help provide closer in-vivo in-vitro correlation or clinically relevant data.”
When the authors drew samples from the NGI at shorter times than usual, representing lower volumes, they found that the fine particle mass (FPM) was decreased, indicating that the aerosol bolus failed to completely transfer through the system, as expected. The ACI, however, appeared to transfer the entire bolus normally, even when sampling times were so short that the sample volume was less than the internal volume of the impactor.
As a result of the anomalous behavior observed, the authors suggest that testing should continue at the 4.0L volume until further investigation with computational fluid dynamics can provide a better understanding of this phenomenon.
Read the abstract. (AAPS members can access full paper)
Read a Melbourn Scientific blog post.
