Impaction-based methods for determining the aerodynamic particle size distributions (APSDs) of aerosolized drug products intended for oral and nasal inhalation are preferred by regulatory authorities because they can be used to directly classify the APSD in terms of the drug substance content of the sampled drug product. One such impactor, the Next Generation Impactor (NGI), is commonly used in the pharmaceutical industry to measure APSD over a calibrated flow rate range. This article has been written to raise awareness of current and evolving approaches to APSD measurement using an NGI. It presents scenarios describing the use of NGI gravimetric cups/inserts during drug development and provides a detailed exploration of their utility in the measurement of APSDs for liquids and dry powders.
Weighing in on NGI gravimetric cups
The article provides a rationale for and examples demonstrating the applicability of NGI gravimetric insert cups for measurement of APSDs of homogeneous liquid suspension and dry particle aerosols. This method can be an alternative or complement to drug-specific NGI or non impaction-based methods to avoid drug-specific assay variability or satisfy regulatory expectations for impaction-based APSD approaches. It may also help address aerosol characterization needs in phase-appropriate product development strategies.