An Assessment of the API Aerosizer® for the Real-Time Measurement of Medical Aerosols from Pressurized Metered-Dose Inhaler (pMDI) Systems

The Aerosizer® is becoming widely used as a rapid method for obtaining aerodynamic particle size distributions of aerosols from pMDls and associated drug delivery devices, as an alternative to more time-consuming methods such as cascade impactors or liquid impingers. It is typically used with purpose-built attachments for sampling the aerosol in a simulated inhalation (Aero Breather ®), and subsequently diluting the sample to the point at which individual particles are separately measured (AeroDiluter1j)). It is possible to obtain an indication of aerosol mass concentration (mass loading), although such data do not necessarily equate to active drug concentration because the technique does not involve a specific chemical assay. Data are presented that indicate that the performance of the Aerosizer,jj) system may be more drug-specific than had previously been thought. In particular, certain pMDIs appear to create such highly concentrated aerosols that meaningful interpretation of mass loading data may not be possible, even with maximum aerosol dilution. The influence of photomultiplier detector voltage on measured size distributions also varies with drug type. While the Aerosizer(R) is a valuable tool for rapid comparative work, there is still a need to compare data with more traditional methods where drug assay is performed in order to be sure that the instrument is set up correctly for the drug being examined.