The transition to low global warming potential propellants in pressurized metered-dose inhalers

First introduced over 70 years ago, pressurized metered-dose inhalers (pMDIs) are well established for the administration of frontline treatments for asthma and COPD. These inhalers contain drug suspended, or dissolved, in a volatile liquid propellant, and make use of the expansion of the propellant to convert liquid formulation into a fine, respirable aerosol. Advantages of pMDIs include their portability, low unit cost, and widespread patient familiarity with basic device operation. However, current pMDIs use hydrofluoroalkane (HFA) propellants, which have high global warming potential (GWP). While HFA propellants emitted by pMDIs are estimated to account for <0.05% of total greenhouse gas emissions, they are nevertheless subject to broad regulatory framework to phase down their use.

The environmental impact of pMDIs has received considerable attention in the Canadian media, but must be balanced with consideration of the needs of patients and healthcare systems. Broadly labeling inhalers as pollutants risks augmenting the social stigma around inhaler use already felt by many patients, particularly adolescents. Simply switching pMDI users to alternative devices, such as dry powder inhalers, fails to appreciate the unique patient needs met by pMDIs, and has led to higher rates of emergency department visits and hospitalizations in at least one well-documented large-scale implementation.

The pharmaceutical industry has been transitioning pMDIs to low-GWP propellants to meet environmental mandates, while aiming to ensure that next-generation devices are available to the millions of patients who rely on pMDIs for effective treatment. The first low-GWP pMDI was approved in the UK in 2025, with additional products expected to soon follow. This presentation will review pMDI design, highlight recent studies demonstrating increased lung deposition for pMDI aerosols, and comment on future research and development needs in the context of the transition to low-GWP propellants.