Use of propellants with high global warming potential (e.g., HFA-134a) for pressurised metered-dose inhalers is being phased down. An alternative is reformulation using propellants with low global warming potential (e.g., HFA-152a), which requires evaluation of the propellant's safety, in particular whether it induces bronchoconstriction or impairs mucociliary clearance (MCC). In this manuscript, we describe two studies, the first comparing the bronchoconstriction potential of HFA-152a vs HFA-134a, the second comparing their effect on MCC.

The bronchoconstriction study was single-dose, randomised, double-blind, controlled, crossover, in adults with asthma. The primary endpoint was relative change from baseline in forced expiratory volume in 1 s (FEV₁) at 15 min post-dose.

The MCC study was multiple-dose (8 days), randomised, open-label, controlled, crossover, in healthy volunteers. The primary endpoint was percent particle retention in the right whole lung at 2 and 4 h after inhalation of radiolabelled particles (PPR₂ and PPR₄).

For the bronchoconstriction study (N = 25), the 95 % CI of the adjusted mean FEV₁ difference between HFA-152a vs HFA-134a at 15 min post-dose was within the −10 % to +10 % equivalence limit (1.86 % [95 % CI –0.48 %, 4.20 %]; p = 0.113). Treatment-emergent adverse events were reported by 4.0 % (HFA-152a) and 12.0 % (HFA-134a) patients, all mild or moderate in intensity, and none serious.

For the MCC study (N = 20), the 95 % CIs for the adjusted mean differences between HFA-152a vs HFA-134a at Day 8 contained 0 for both PPR₂ (1.36 [–2.28, 4.99]%; p = 0.442) and PPR₄ (0.70 [–1.73, 3.12]%; p = 0.553). A similar proportion of subjects had treatment-emergent adverse events (25.0 % vs 35.0 %), all mild in intensity, and none serious.

These two studies suggest a switch in propellant from HFA-134a to HFA-152a is unlikely to induce post-dose bronchoconstriction in asthma or impact lung MCC, and is not accompanied by any safety concerns.