A Priori Formulation Design of Solution Metered Dose Inhalers with Next Generation Propellants
Lewis DA, Lewis DI, Carter J, Young PM, Johnson R, Ong H, Zhang L.
Respiratory Drug Delivery 2025. Volume 1, 2025: 66-71.
Abstract:
Building upon established principles for the design and prediction of solution metered dose inhaler (MDI) performance, this study refines and expands key semi-empirical equations for predicting mass median aerodynamic diameter (MMAD) and ex-valve fine particle fraction (FPF) to incorporate the low global warming potential (GWP) propellants HFA-152a and HFO-1234ze. Using a melatonin formulation as a case study, we demonstrate the successful delivery of sub-micron aerosol particles using these new propellants, confirming their viability as environmentally sustainable alternatives. Through detailed in vitro characterization with Next Generation Impactor (NGI) and Micro-Orifice Uniform Deposition Impactor (MOUDI), we provide updated predictive tools that enhance the ability to control and optimize MDI performance. This work extends the ‘armchair’ formulation design approach established in previous research, enabling efficient development of solution MDIs with targeted delivery characteristics, as exemplified by the successful systemic delivery of melatonin, validated by clinical proof-of-concept.
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