Translated impact on carbon footprint from choice of inhaled therapy: a Danish scenario

To the Editor:

With increasing climate change, all sources of greenhouse gases must be considered. Hydrofluorocarbon (HFC) propellants are used in all pressurised metered dose inhalers (pMDIs) and, although they are not as ozone-depleting as the earlier chlorofluorocarbons (CFCs), they are potent greenhouse gases and there is a general ask for reduction in their use [1]. In this respect, respiratory doctors indirectly affect climate change through their prescription patterns [2], something only few are aware of, and which may be difficult to translate and explain to patients. To illustrate the impact of switching from pMDIs to dry powder inhalers (dMDIs) we wanted to compare climate impact of inhaler switching to climate costs of well-known items and activities in Denmark, a country with a population of 6 million inhabitants.

Information on number of metered dose inhalers (MDIs) and pMDIs, and thus doses, in 2019 (pre-COVID-19) was obtained from the Danish Statistical Registry of Medication (DSRM). This register covers all dispensed drugs in Denmark. The pMDIs dispensed accounted for 28 million defined daily doses (DDD). The Global Warming Potential (GWP) indicates the global warming impact of a climate pollutant compared to CO₂, with CO₂ having a GWP of 1 and GWP for all other gases are multiplications of this. GWP thereby reflects the difference in heating impact and lifetime of different climate pollutants, such as HFCs, in the atmosphere compared to CO₂. GWP is expressed for a given time period; GWP20 indicates impact in a 20-year time horizon. With an average emission of about 256 mg HFC per DDD (according to the Danish Medical Agency, access to documents in 2021) this caused about 7.2 tonnes of HFC emission in 2019. According to the DSRM, approximately 90% was HFC-134a (GWP20 4140); i.e. 1 kg of HFC-134a causes on average the same warming as 4140 kg of CO₂ seen over a 20-year period. The remaining 10% was HFC-227ea (GWP20 5850), corresponding to a climate impact of approximately 31 000 tonnes of fossil CO₂ (over a 20-year period).

The conversion of climate benefits from partial switching to HFC-free powder inhalers was compared to diesel consumption, electricity consumption in detached houses, and production of jeans using the following calculations. According to the US Environmental Protection Agency, 1 L of diesel emits approximately 2.69 kg of CO₂ [3]. We used official Danish information on average use of electricity in a detached house. A family consisting of two parents, a teenager and two younger children living in a 180-m² detached house, not heated by electricity, consume approximately 5351 kWh a year according to the Danish Energy Agency [4]. Electricity can be “translated” into an equivalent amount of CO₂, and according to the Danish environmental declaration on electricity, 1 kWh emitted 0.171 kg CO₂ equivalents in 2019 [5], which brings the emission of the house to: (5351 kWh × 0.171 kg CO₂ equivalents)/kWh=915 kg CO₂ equivalents per year. Regarding the climate impact of a pair of jeans, Oxfam announced in 2022 that approximately 33 kg of CO₂ equivalents are emitted over the life cycle of a pair of jeans with half of it required for the actual production of one pair of jeans [6]. We used the figure of 33 kg CO₂ equivalents per year to convert HFC savings to pairs of jeans.

On an individual level, shifting a patient from a pMDI containing HFC-134a to a dMDI will lead to a saving of 390 CO₂ equivalents per year (GWP20); i.e. a patient will every year reduce his/her climate impact with the same magnitude as emitting 390 kg less CO₂ seen over a 20-year warming period. Similarly, shifting from an HFC-227ea to a dMDI will lead to a saving of 550 CO₂ equivalents. By replacing HFC-134a MDIs with dMDIs in an individual patient using 4 puffs per day, the achieved annual climate benefit corresponds to the climate impact of 145 L of diesel; the corresponding figure for HFC-227ea inhalers would be 204 litres. The impact of this will vary according to car model and driving needs, but in Denmark the average consumption for a family car is 1000 L per year.

Similarly, the savings on a national level can be calculated. Table 1 shows the benefits per year for three different levels of reduction of the market share of pMDIs. Currently, pMDIs have a market share of approximately 20%, and the suggested absolute reductions represent relative reductions of 25, 50 and 75%, respectively.

A large part of inhaler choice is down to habit. Denmark consists of five administrative regions, with slightly different patterns of inhaler use. If the four regions with the highest use of pMDIs had a pattern of pMDI/dMDI use similar to that of the region with the lowest use of pMDI (the Region Zealand), this would be comparable to a saving of 3634 CO₂ equivalents (GWP20) – or what can be translated to 1 350 000 L of diesel, electricity for 4000 detached houses, or 110 000 pairs of jeans.

These figures merely illustrate the scale of reduction in CO₂ equivalents that can be achieved. We have used crude data, a uniform use of 4 puffs daily of pMDIs, and we have assumed that all dispensed drugs are used. Indeed, the climate impact of pMDIs would be reduced if all dispensed pMDIs would be used completely before being disposed of. We are also very aware that we have not done proper lifecycle assessment for the inhalers currently on the market in Denmark. The dMDIs most frequetly used in Denmark are the Easyhaler, Turbuhaler, Nexthaler and Ellipta devices. Nevertheless, the notion that “inhalers contribute very little to climate anyway” is no longer valid. The climate benefits in our report are of the same magnitude as those presented by Wilkinson et al. [7] and Janson et al. [8].

Treatment costs for society and patients do not necessarily increase by replacing the climate damaging pMDIs with dMDIs. For many reasons, it is not possible to replace pMDIs with dMDIs for all patients. Particularly, frail elderly patients will likely only benefit from pMDIs in volume spacers or nebulisers. Most importantly, health professionals should match the device to the patient's capability to perform the specific inhalation manoeuvres recommended for the device and choose a device that has performance–capability information for the specific age group of the patient [9, 10]. In this regard, soft mist inhalers and nebulisers are also options when trying to choose more climate-friendly inhaler options. Also, new pMDI propellants with much lower GWP, HFC-152a and HFO-1234ze(E), are under development and the first pMDI with lower GWP may be launched in 2025 [11].

Few studies have reported on changing patients’ inhalers, but data from a large effectiveness trial indicate that changing patients to a dMDI can benefit both patients and the environment [12]. Any change in inhaler will need careful consideration and an open discussion between the healthcare professional and the patient, with patient preference being an important part. Currently, we believe many healthcare professionals could be holding back on information regarding impact on inhalers on climate, most probably because they find the information is difficult to make understandable to patients, but possibly also as a result of a belief that patients should not be blamed for the climate crisis. Of course, they should not – but prescribing physicians who do not take climate impact into consideration when informing patients and prescribing MDIs should.

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