Together with delivered dose, aerodynamic particle size distribution (APSD) is typically identified as a Critical Quality Attribute (CQA) for orally inhaled and nasal drug products (OINDPs) making it a primary focus for in vitro characterisation. The APSD of an OINDP defines how particles behave in a moving air stream. It is intuitively relevant to the understanding of likely lung deposition and hence potential drug efficacy. Typically particles should be in the range of 1 to 5 microns to be effective, any larger than 5 microns and they are likely to impact the oropharynx and be swallowed, any smaller than 1 micron and it is possible that the particles will remain entrained in the air system.

One of the four Critical Quality Attributes (CQAs) that determine the safety, quality and efficacy of orally inhaled and nasal drug products (OINDPs), delivered dose is the total amount of drug emitted from the drug device that is available to the user, when the device is actuated correctly. The uniformity of the delivered dose, or DDU, must be ensured within and between devices. DDU is measured by firing the test device into a sampling apparatus which contains a filter. The active drug caught on the filter is then dissolved in solvent and analysed using High Pressure Liquid Chromatography (HPLC). Depending on the type of OINDP under test, different apparatus set-ups are required.

Making a relatively small investment in systems that enhance the clinical realism of standard pharmacopoeial in-vitro test set-ups for delivered dose uniformity (DDU) testing and aerodynamic particle size distribution (APSD) measurement may help bridge the gap between data collected during QC testing and in vivo performance helping to accelerate and improve R&D.