The phase-out of chlorofluorocarbons for use in propellant-based metered dose inhalers (pMDIs) has completed. This has not only had positive impacts on stratospheric ozone levels, but has reduced the emission of gases with global warming potential (GWP) by an amount similar to the annual emission of carbon dioxide produced by burning fossil fuels at the start of this decade to generate heat and electricity. However, the replacement propellants are hydrofluorocarbons (HFCs) still with significant GWP. As such, they are now considered within the basket of gases (F-gases) whose phase-down will be managed under the 2016 Kigali Amendment to the Montreal Protocol, which came into effect on 1st January 2019.
The emissive use of pMDIs contributes only a small percentage of F-gas emissions today but this will change as other uses are eliminated. There are now pressures from many different sources, including NICE[i] to move to inhalers with lower carbon footprint. At the same time, the cost of HFCs will increase and availability of pharmaceutical grade propellant will decrease with a reduction in other applications. Without an affordable alternative to deliver rescue medication, pMDIs will remain essential. Whilst not-in-kind alternatives appear to be too expensive, alternative propellants with low GWP are required. One candidate, HFC 152a is in active development with encouraging results.
[i] National Institute for Health and Care Excellence (2019). Patient Decision Aid. Inhalers for Asthma.