Pressurised metered-dose inhalers (pMDIs) are a lifeline for millions with asthma and chronic obstructive pulmonary disease (COPD), yet their environmental toll is drawing increasing attention. These devices rely on hydrofluorocarbon (HFC) propellants, potent greenhouse gases that can have a climate impact equivalent to a small car driving 175 miles per use. With the NHS prescribing pMDIs for 70 per cent of its inhaler needs, the healthcare sector is now racing to curb this carbon footprint without compromising patient care.
The NHS Long Term Plan has set ambitious goals to slash emissions, targeting a shift towards lower-carbon alternatives like dry powder inhalers (DPIs), improved disposal methods, and the development of propellants with lower global warming potential (GWP). Experts estimate that moving just 30 per cent of pMDI users to DPIs could reduce emissions by 374 kilotons of CO₂ equivalent (ktCO2e) each year. Paul Hardman, Managing Consultant at Broughton, a firm specialising in inhalation testing, said: “The pharmaceutical industry can address these challenges by investing in research for low-GWP propellants.” His insight underscores a growing push for sustainability in respiratory care.
Historically, inhaler propellants have evolved under global pressure. The Montreal Protocol in the 1980s phased out chlorofluorocarbons (CFCs) due to their ozone-depleting effects, ushering in HFCs as a safer alternative. However, HFCs trap heat in the atmosphere far more effectively than CO₂, lingering for years and amplifying global warming. The Kigali Amendment, an international agreement, now targets HFCs for reduction, prompting the medical sector to rethink its reliance on these gases.
DPIs offer a compelling alternative. Unlike pMDIs, they use no propellants, delivering medication via a patient’s own breath. The powder, stored in blisters, is dispersed into the lungs when inhaled, cutting out HFCs entirely. Yet, this solution has limits. Hardman noted that “some patients, typically the very ill, elderly or very young, will be unable to generate sufficient inspiratory flow to correctly use a DPI.” For these groups, pMDIs remain essential, despite their higher cost and environmental impact.
Innovation is stepping in where DPIs fall short. Low-GWP propellants like HFC 152a and HFO 1234ze(E) are emerging as viable substitutes. Pharmaceutical giants AstraZeneca and Chiesi are spearheading efforts to integrate these into pMDIs, with launches expected by late 2025. HFO 1234ze(E), in particular, stands out for its low GWP and physical similarities to HFC 134a, a widely used propellant, easing the redesign process for manufacturers.
The regulatory hurdles are significant. The transition to new propellants faces rigorous oversight from bodies like the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA).
- The FDA’s Guidance for Industry demands toxicological assessments and proof of safety and effectiveness.
- The EMA’s Guideline on the Pharmaceutical Quality of Inhalation and Nasal Products requires detailed studies on drug delivery and device compatibility.
Past shifts, such as the move from CFCs to HFAs in the 1990s, involved extensive in-vitro and in-vivo trials to ensure performance. Similar scrutiny awaits these new options, with manufacturers testing for extractables and leachables to rule out toxic contamination risks.
Collaboration could speed up this shift. Partnering with specialist firms, companies can streamline development and navigate regulatory mazes more effectively. Still, the patient remains the priority. Any new inhaler must deliver consistent, effective treatment, balancing environmental gains with clinical needs. Hardman emphasised, “It is critical to examine how the new propellants interact with existing formulation components, such as active pharmaceutical ingredients and excipients.”