Improving the Sustainability of Pressurised Metered Dose Inhalers
Since their introduction in 1956, pressurised metered dose inhalers (pMDIs) have become the dominant treatment choice for patients suffering from common respiratory diseases such as asthma and chronic obstructive pulmonary disease (COPD). However, unbeknown to most patients and many doctors, pMDIs account for 3.9% of NHS’s annual carbon emissions.1 Here we will discuss how formulation changes might be the answer to the pMDI-related sustainability problem.
The role of propellants in a pMDI system is to provide the required pressure to atomise the drug formulation into a micron-scaled aerosol, allowing for effective delivery into the lungs. Due to their well-established toxicological profiles and ideal physical properties, when initially developed, pMDIs utilised chlorofluorocarbons (CFCs) as the propellants of choice. Fast-forward to 1987, however, and CFCs were soon to be replaced; the Montreal Protocol was signed, banning the use of CFCs due to their depletion of stratospheric ozone.2 Although pMDIs were technically exempt from the legislation as essential medicinal devices, the use of CFCs as propellants was halted just a few years later.
In place of CFCs came a group of compounds known as hydrofluorocarbons (HFCs) – molecules that make for similarly effective pMDI propellants but without the effects on the ozone layer. The cost to pharmaceutical companies of developing these new formulations, alongside accompanying hardware, manufacturing processes and clinical data, was hundreds of millions of dollars. Now, it seems, they will have to do it all over again.
The Problem with HFCS
The shift from CFCs to HFCs across all industries resulting from the Montreal Protocol was not just beneficial to the ozone layer; it also represented a seismic decrease in global carbon emissions of approximately 11 gigatonnes between 1985 and 2010.3 While leaving CFCs in the past was certainly an improvement, HFCs are still potent greenhouse gases (GHGs), with global warming potentials (GWPs) of up to 3,350 times that of CO2. 4 These gases can survive for long periods in the upper atmosphere, contributing to the rise in global temperatures. HFCs are part of a basket of what’s known as fluorinated gases (F-gases), all known to be powerful GHGs. The EU began regulating their use back in 2006, setting out targets for a reduction. This was followed by an amendment to the Montreal Protocol in 2016, known as the Kigali Amendment, which sought to regulate the phase-out of HFCs altogether.
In reality, the majority of F-gas emissions come from other applications, such as refrigeration, not pMDIs – in fact, their use constitutes just 2.3% of global F-gas emissions.4 Nevertheless, the need to phase out the use of HFCs in pMDIs remains, especially as demand for inhaled therapeutic medicines grows with increasing population sizes and disease prevalence. This need has already been recognised in the UK, for example, where the NHS laid out plans to reduce the usage of high GWP pMDIs in its Delivering a ‘Net Zero’ National Health Service report.5
