Principles for a patient-centred transition to low-global warming potential pressurised metered-dose inhalers

Climate change is recognised by the World Health Organization (WHO) as a major global health threat 1 ; people living with chronic respiratory diseases, such as asthma and chronic obstructive pulmonary disease, are disproportionately affected due to declining air quality and changes in allergen patterns 2 , 3 . Inhaled medicines are the mainstay treatment for patients with chronic respiratory diseases 4 . They are most often delivered via pressurised metered-dose inhalers (pMDIs) with salbutamol pMDI being the most widely used inhaler in the world 5 , 6 . Most current pMDIs use hydrofluorocarbon (HFC) propellants, namely hydrofluoroalkane (HFA)-134a and HFA-227ea, to deliver the medicine into the lungs of patients 5 , 6 . In respiratory medicine, these HFC propellants are most commonly referred to as HFA propellants; therefore, the term HFA is used throughout this manuscript. While HFAs do not contribute to ozone depletion like their predecessors chlorofluorocarbons, HFCs are potent greenhouse gases with high global warming potential (GWP) 7 , 8 , and this has led to their phase-down under the Kigali Amendment to the Montreal Protocol, and regional F-gas regulations in Europe and the USA 3 . For example, the carbon footprint of the currently available salbutamol pMDI with HFA-134a (GSK) is approximately 27 kg CO 2 e over the complete lifecycle of the inhaler 9 ; this is largely due to the propellant which has a 100-year GWP (GWP100) of 1530 8 . While propellant-free dry-powder inhalers (DPIs) or soft-mist inhalers have negligible carbon footprints 5 , 10 , not all patients are able to use these and not all products are available in these devices. In real-world practice, pMDIs also appear to be preferred by some patients for reliever inhalers such as salbutamol, with prescriptions comprising >50% of all inhalers, exceeding those for DPIs 5 , 6 , 11 , 12 . In addition, salbutamol pMDIs are often favoured by payers due to their lower commercial pricing; however, cost considerations should be balanced with clinical appropriateness and patient needs to ensure patient-centred treatment decisions 6 .