| A decade after the initial development of the NGI, Mark Copley of Copley Scientific considers its origins and its subsequent impact on the pharmaceutical industry
Cascade impaction data are used to validate the performance of every pharmaceutical inhaled product. Cascade impactor use within the pharmaceutical industry has therefore increased substantially in recent years as the sector has moved to exploit the pulmonary route for drug delivery. Towards the end of the last decade, a consortium of pharmaceutical companies was formed in order to develop an impactor specifically tailored to inhaler particle size characterisation. The result of this collaborative investment was the next generation pharmaceutical impactor (NGI).
Ten years after work began on the NGI, this article examines the criteria used in its development, the key design features of the instrument, and its calibration and performance. Alongside this, the important characteristics of the Andersen cascade impactor (ACI) – the other primary impactor specified in the US and European Pharmacopoeias for inhalation product testing – are also reviewed. Factors influencing the commercial use of both the ACI and NGI are considered.
DEFINING THE PROBLEM – THE STARTING POINT FOR THE NGI
Cascade impaction is uniquely valuable for inhaled product characterisation because it provides size distribution data specifically for the active pharmaceutical ingredient, rather than for the overall formulation. In addition, it is a technique based on the measurement of aerodynamic particle size diameter, a parameter that is intuitively relevant for inhalation product measurement. A limitation of cascade impaction is its time-consuming and manually-intensive nature.
Before the introduction of the NGI, the ACI was the main impactor used by the pharmaceutical industry. Although originally designed for microbial air sampling, the ACI is a well-established instrument that has served the industry well. It remains in widespread use and is expected to do so into the foreseeable future. One drawback, however, is its configuration, which is poorly suited to automation as a route to improved measurement productivity. Total analysis time and automation were important issues for the project, and other design criteria were also shaped by limitations associated with the ACI, including: |
