The essential role of pMDIs
Over 500 million people globally live with respiratory disease such as asthma or chronic obstructive pulmonary disease (COPD).1,2 Inhaled medicines are critical for treating respiratory disease worldwide, and are recommended in all global treatment guidelines.2,3 Pressurised metered dose inhalers (pMDIs) comprise an integral component in the respiratory medicine toolbox, used for both maintenance and rescue medication, across all stages of disease severity.2,3 These inhalers are affordable (particularly important in developing countries) and are the most widely available and commonly used inhaler type, accounting for 78% of inhaler use globally.4 Some are on the World Health Organization Essential Medicines List.5 Pressurised MDIs are also critical for certain vulnerable populations, including children younger than 10 years,6 those suffering from acute lung attacks,2,3 those with low inspiratory capacity (e.g. elderly patients)7 and those from low and middle income countries.8
The importance of pMDI choice
Selection of the most appropriate treatment is dependent on both the choice of drugs and inhaler device.23 Inhaler devices and the medicines contained within them are not inter-changeable.23 In the era of personalized medicine, different alternatives are needed – one size does not fil all. Switching devices without considering all personal factors leads to loss of asthma control and risk of serious attacks,23 both of which are associated with higher carbon footprint due to increased health resource utilization.24
A combination of disease and patient variables should influence inhaler selection in clinical practice.25
pMDI propellants – the transition to greener alternatives
Medical propellants are essential for appropriate delivery of medicines to the lungs and are thus an integrated part of an effective inhaled medicine. Per- and polyfluoroalkyl substances (PFAS), commonly used as propellants in pMDIs, are a group of synthetic compounds that contain a stable and inert C-F bond.26 Used for medical purposes, fluorinated gas propellants currently account for a small proportion of global greenhouse gas (GHG) emissions (<0.1%).27 Used as propellants in pMDIs, currently approved PFAS (e.g. HFA-227ea and HFA-134a) are responsible for 0.04% of total global GHG emissions. A number of pMDI manufacturers are developing greener alternatives. These greener propellants (e.g. HFO-1234ze and HFA-152a) are on track to become available from the end of 2025 which will bring emissions down to near 0%.28,29 For example HFO-1234ze has a 99.9% lower global warming potential than propellants used in currently available inhaled medications, bringing the carbon footprint of pMDIs using this propellant within the range of dry powder inhalers.28 HFO-1234ze is not persistent, bioaccumulative or toxic.30–38
