In-vitro evaluation of pMDI spray development of HFA134a, HFA152a and HFO1234ze(E)

To assist the transition to alternative low GWP pMDI propellants, the current study performed high- speed imaging and droplet sizing of the near-orifice spray development of HFA-152a and HFO- 1234ze(E) based formulations. Conventional HFA-134a propellant was tested as the control. Placebo (pure HFA/HFO) and model solution (2 mg/mL drug dissolved in 8%w/w ethanol) formulations were measured, for each propellant. The results indicate larger droplets produced by HFA-152a and HFO- 1234ze(E) based placebo formulations at the near-orifice locations. HFA-152a also showed a wider and denser spray profile as compared to that of HFA-134a due to its low vapour pressure and density. The temporal spray development was also less stable and repeatable. HFO-1234ze(E) showed a similar spray profile and a more stable spray development compared to that of HFA-134a, however with reduced spray repeatability. The impact of changing propellants on spray development was reduced in model solution formulations. Both HFA-152a and HFO1234-ze(E) showed comparable spray profiles and measured droplet size to that of HFA-134a. The issue of low spray stability and repeatability persists in solutions, particularly for HFA-152a. These early results indicate that the transition to low GWP propellants is feasible, but further optimisation of the actuator design and formulation composition is needed.