Pressurised metered dose inhalers account for nearly all inhaler-related carbon emissions in Australia despite representing fewer than half of prescribed inhalers.
Research by a team of Perth respiratory physicians has reignited calls to favour greener inhalers like dry powder or soft mist inhalers when clinically appropriate.
The investigators analysed over 121 million inhaler reimbursements over a 10-year period from 2013-2023, finding pressurised metered dose inhalers (pMDIs) made up 47.5% of prescriptions, but generated 95.6% of inhaler-related emissions.
PBS data showed a 28.3% increase in inhaler reimbursements overall, with the proportion of pMDIs prescribed remaining stable across the decade (47.2% in 2013 vs 48.5% in 2023).
These devices made up 41.8% of inhaled corticosteroid and long acting beta agonists (ICS-LABA) and 77.5% of ICS monotherapy, the researchers noted.
However, single inhaler triple therapy prescribing shot up from 71,000 in 2018 to more than 1 million in 2023, of which 87% were delivered by dry powder inhalers.
Reliever inhaler prescribing increased by 34.5% over the 10 years, delivered almost entirely by pMDIs (97.9%) with short-acting beta agonists (SABA) making up the majority of prescriptions (>96.0% of relievers until 2020).
But there was shift in reliever prescribing patterns from 2020, with a decrease in SABA pMDIs (87.5% in 2023) and an increase in dry powder inhaler prescribing (1.1% to 8.1% in 2023), mostly represented by ICS-formoterol therapy (79.6%).
This aligned with a change in Australian and international guidelines in 2019, which recommended ICS-formoterol over SABA as first line anti-inflammatory reliever (AIR) therapy or as maintenance and reliever therapy to improve asthma control, reducing reliance on relievers and in turn reducing carbon emissions, the researchers said.
“Inhaler-related CO2e (equivalent) emissions in Australia are largely driven by pMDIs. Transitioning toward non-pMDI inhalers where clinically appropriate offers an opportunity to reduce emissions without compromising care,” the researchers wrote in a research letter for Chronic Respiratory Disease [link here].
“…pMDIs in Australia contain hydrofluorocarbon (HFC) propellants (HFC-134a or HFC-227ea), which are potent greenhouse gases generating approximately 20 times more carbon emissions than dry powder inhalers or soft mist inhalers.”
They added that improvement in the diagnostic accuracy of airways disease, reducing reliance on reliever inhalers through better disease control, and adopting an AIR-based approach in asthma management were other greener strategies that should be implemented.
A major limitation of the study was that the analysis excluded over-the-counter sales and private prescriptions due to a lack of data, which underestimated the proportion of SABA and pMDIs prescribed nationally. The authors said over-the-counter salbutamol sales were believed to account for 70% of total salbutamol inhalers sold annually.
They suggested creating a national database that captured over-the-counter and private sales to inform national policies and guide reduction in inhaler-related emissions.