Prediction of the Aerosol Performance of Active Solution and Suspension Formulation pMDIs using a 1-dimensional Thermofluid-Mechanic Model

J. A. Thorne1, D. P. J. Cotton1, S. B. Kirton2, M. Knowles1, K. C. Lee3, D. Murnane2, A. I. Sapsford1, A. D. Wright1

1Recipharm, Bergen Way, King’s Lynn, PE30 2JJ, U. K.

2University of Hertfordshire, College Lane, Hatfield, Hertfordshire, AL10 9AB

3University of East London, Docklands Campus, University Way, London, E16 2RD


A thermofluid mechanic model to predict the aerosol performance of pressurised metered dose inhalers (pMDIs) was developed and used to predict the droplet size distribution generated for a range of pMDI valve and actuator configurations. An experimental study was also conducted to measure the droplet size distributions of the same pMDI valve and actuator configurations using laser diffraction, and proof of principal next generation impactor (NGI) stage performance testing, to establish links between aerosol droplet and residual particle sizes. Experimental measurements were taken for both suspension and solution formulations of fluticasone propionate (FP) in R134a propellant, where solution formulations incorporated ethanol at 15 % w/w. For both formulations, FP was present at a 0.07 % concentration w/w. The suspension formulation results show good agreement between the simulation-derived droplet sizes and those obtained via laser diffraction. The simulation data follow the trend exhibited by the experimental data in terms of the effect of spray orifice diameter on droplet size. For the smaller orifice diameter case, the solution formulation simulation data agree very well with experimental results. However, a significant discrepancy is observed for the results obtained from the larger actuator orifice diameter case, indicating the significant effect of ethanol on the flashing properties of the formulation during spray generation.


Key Message

A thermofluid mechanic model to predict droplet sizes from pMDIs is presented, alongside experimental measurements of droplet size and residual particle size.