The impact of inlet design on HFA-152a pMDI drug delivery

When assessing aerodynamic particle size distribution (APSD) using the Next Generation Impactor (NGI), throat model selection can significantly influence drug deposition outcomes. Accurate deposition data is essential for optimising pMDI design and ensuring consistent, effective drug delivery to patients.

Recent research by our pulmonary/pMDI experts—Aaron Taylor, Chad Haraldson, and Stephen Stein at Kindeva—explores how United States Pharmacopeia (USP), oropharyngeal cast model (OPCM) and large volume chamber (LVC) inlets affect particle size measurements in HFA-152a solution pMDIs with varying ethanol concentrations.

Here were the key insights from the research:

• Inlet geometry drives deposition: The OPCM throat captured more large droplets, leading to lower fine particle fractions and artificially smaller measured MMADs.
• Ethanol concentration effects: As ethanol levels increased, throat deposition rose — most notably in the OPCM throat, which showed minimal sensitivity to ethanol changes compared to the USP inlet.
• LVC as a baseline: The 20L expansion chamber minimized throat interference, allowing a more accurate representation of initial droplet size and aerosol behavior.

This data underscores the importance of throat model selection in formulation development and in vitro characterization. Aligning test methods with real-world delivery dynamics improves product performance assessment and the relevance of in vitro data to clinical outcomes.

Want to dive deeper into the data? View the full poster presentation.

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