Switching to Dry Powder Asthma Inhaler Better for Climate Change, Researchers Say

Researchers in the United Kingdom compared the potential impact on carbon footprint and asthma symptom control of switching maintenance therapy to a dry powder inhaler vs continuing with a metered dose inhaler containing hydrofluorocarbon propellant.

Switching from a pressurized metered dose inhaler (pMDI) to a dry powder inhaler (DPI) for maintenance therapy more than halves the carbon footprint of individuals with asthma, without making the disease worse. The UK study was published in the journal Thorax.

The use of chlorofluorocarbons (CFCs) in aerosol propellants was banned under the 1987 Montreal Protocol agreement because of their impact on global warming. In addition, the authors noted, there is a greater interest among health care organizations in reducing their carbon footprint due to the known negative impacts of climate change on human health.

While the hydrofluorocarbons that replaced CFCs in pMDIs don’t deplete the ozone layer, they are potent greenhouse gases, and their emissions comprise 3% to 4% of the total carbon footprint associated with health care in the United Kingdom, the researchers said.

Using data from the Salford Lung Study in Asthma, researchers carried out a secondary post hoc analysis to compare the potential impact on carbon footprint and asthma symptom control of switching maintenance therapy to a DPI vs continuing with a pMDI containing hydrofluorocarbon propellant.

The post hoc analysis was based on a subset of 2236 (53%) patients from the Salford Lung Study in Asthma who, at baseline, were using a pMDI. The Salford Lung Study was a 12-month, open-label, primary care study in which adults with symptomatic asthma who were taking inhaled corticosteroids (ICS) or ICS/long-acting beta-agonists for maintenance therapy were randomized to either a combination of fluticasone furoate/vilanterol (FF/VI) via the Ellipta DPI or to continue their usual care as prescribed by their general practitioner. The Ellipta device is marketed by GlaxoSmithKline, which funded the studies.

In the secondary analysis for the current study, patients using pMDIs (n = 1081) were randomized to FF/VI via the Ellipta DPI or continued their usual therapy (n = 1155) with a pMDI.

Participants were matched for demographic characteristics, symptom serverity, and baseline Asthma Control Test (ACT) total scores. The mean age was 49 years; the mean ACT score was 16.6 in the usual care group and 16.5 in the FF/VI group.

Symptom control was assessed at the start of the study, and after 12, 24, 40, and 52 weeks, using the ACT. Researchers calculated annual carbon dioxide emissions (CO2e kg) for the total number of maintenance and rescue inhalers prescribed over 12 months.

Results showed that annual CO2e kg per patient (maintenance plus rescue therapy) was significantly lower with FF/VI DPI treatment (ie, the patients who switched) compared with those who continued with their usual care (least squares geometric mean, 108 kg [95% CI, 102-114] vs 240 kg [95% CI, 229-252]; P < .001).

Asthma control was consistently superior over the 12 months in the FF/VI DPI group compared with the usual care group, although control improved in both treatment arms.

By week 24, the odds of responding well to treatment in the switch group were around double those in the usual care group, and this difference persisted over the entire 12 months.

Those who switched were prescribed around 1 fewer rescue salbutamol metered dose inhaler than those who continued on usual care (7.2 vs 8).

The researchers calculated that the annual carbon footprint saving for each patient who switched was 130 kg CO2e. After a year, annual CO2e amounts for each person in the switch group were less than half those of the usual care group: 108 kg vs 240 kg.

Although patients were allowed to change inhalers during the study, most stuck with the type to which they had been assigned: 80% remained on the pMDI in the usual care group and 85% remained on a DPI in the switch group.

The large carbon footprint caused by the use of hydrofluorocarbon propellants in pMDIs in the United Kingdom is 3 times that in Europe and a switch to a greener option should be encouraged, said the researchers.


Woodcock A, Janson C, Rees J, et al. Effects of switching from a metered dose inhaler to a dry powder inhaler on climate emissions and asthma control: post-hoc analysis. Thorax. Published online February 7, 2022. doi:10.1136/thoraxjnl-2021-218088