Impact of choice of inhalers for asthma care on global carbon footprint and societal costs: a long-term economic evaluation.

BACKGROUND: While effective asthma control medications reduce the burden of asthma, a significant subgroup of these treatments, namely metered-dose inhalers (MDIs), produce substantial greenhouse gas (GHG) emissions, thus contributing to climate change. This study quantified the global climate impact (i.e. carbon dioxide equivalent [CO2e] emissions) and costs of long-term status quo asthma inhaler use versus alternative scenarios substituting MDIs with propellant-free dry powder inhalers (DPIs). METHODS: Three scenarios were evaluated across 10-year (2020-2030) and 50-year (2020-2070) time horizons: A (status quo inhaler use), B and C (2% and 5% year-over-year substitution of MDIs with DPIs, respectively). Global inhaler volumes and costs at baseline were sourced from IQVIA, then projected using UN and WHO trends in per capita GDP, urbanization, and asthma population growth. Inhaler spending was assumed to fall by 90% following generic entry in 2030. The carbon footprint per inhaler and health damage factors for disability-adjusted life years (DALYs) were derived from literature. The US government's central and high-impact estimates for the social cost of carbon (SCC) were used to calculate emissions costs. RESULTS: Over 50 years, scenario A resulted in 826 million tonnes of CO2e emissions globally, with an associated SCC between 21% and 65% of the projected global spending on asthma inhalers. In comparison, CO2e emissions were reduced by 38% and 58% in Scenarios B and C, respectively, and DALYs improved by 33 and 51%. Depending on SCC estimates, Scenarios B and C increased global costs by 7.3% and 16.5%, respectively (central SCC), or decreased costs by 4.2% and 2.6% (high-impact SCC) versus Scenario A. Over 10 years, Scenario A resulted in 97 million tonnes of CO2e emissions globally, with an associated SCC between 4.4% and 12.2% of projected spending. In comparison, Scenarios B and C were associated with 12% and 24% reductions in CO2e emissions and improvements in DALYs by 11.5% and 22.7%, respectively. CONCLUSIONS: Global efforts by environmental and health-policy decision-makers to substitute currently available MDIs with DPIs for asthma control would result in substantial reductions in GHG emissions with manageable costs, or potential cost savings, depending on the SCC. Policies that decrease use of MDIs warrant global attention.