We conducted a series of optical and X-ray scattering experiments to assess the performance of low-global warming potential replacement propellant P-152a in a pressurised metered dose inhaler spray. Measurements of droplet size, spray density and spreading angle were conducted on both P-152a and P-134a sprays both in pure form and in a solution of 3.38 µg/µL ipratropium bromide in 15% v/v ethanol co-solvent. The P-152a formulations produced less dense sprays with statistically similar primary droplet size. The density difference correlates with the relative reduction in liquid density between the propellants. The P-152a sprays are visibly wider with a larger opening angle, but X-ray data reveal little difference in the width of the projected mass profiles. This suggests that while P-152a sprays produce a wider dilute droplet field around the core of the spray, the structure of the potential core at the nozzle exit remains similar. The presence of ethanol co-solvent in the solution formulations was found to somewhat ameliorate the effect of switching the propellant.
Switching pMDI solution formulations of ipratropium bromide from P-134a to P-152a propellant under otherwise identical conditions results in a wider, less dense spray, with little change in primary droplet size. The presence of an ethanol co-solvent moderates the effect of switching propellants relative to a pure propellant spray.