Metered Dose Inhalers (MDIs)

Inhaled therapy is essential for the treatment of asthma and chronic obstructive pulmonary disease (COPD). There are two main types of inhalers for the delivery of respiratory drugs: the metered dose inhaler (MDI), which uses HFCs as the propellant and the dry powder inhaler (DPI). The choice of the most suitable inhaler is a complex decision taken between doctor and patient. A minority of patients (10-20 per cent or less), notably the very young and very old, cannot use available alternatives to HFC MDIs. These patients generally cannot use dry powder inhalers. This is because a strong breath is needed to inhale the drug within the inhaler.

HFC based MDIs were introduced in the EU 1994 to replace CFCs, and by 2006 in the EU most MDIs used contained HFCs and there are now HFC MDIs available to cover all key classes of drugs used in the treatment of asthma and COPD. MDIs have been subjected to extensive regulatory assessments for safety, efficacy and quality. Clinical trials have shown HFC MDIs to have a safety and efficacy profile comparable to that of CFC MDIs that they replaced. Furthermore, HFC-containing MDIs may even provide improved performance resulting from more consistent dosing.

The number of patients using HFC based asthma inhalers in the EU is estimated to be at least 5 million.

The F-Gas Regulation 517/2014 recognises the importance of HFCs for use in Metered dose inhalers and makes sure they will remain freely available for this use.

Why are HFC-134a and HFC-227ea used –important properties for MDIs

  • Very low toxicity
  • Non-flammable
  • Boiling range (-10 to –30ºC)
  • Acceptable solvent behaviour
  • Chemically stable
  • Acceptable to patients in terms of taste and smell

Approximately 690 million HFC MDIs (with an average 15g HFC/MDI) are currently manufactured annually worldwide, using about 10,300 tonnes of HFCs and accounting for a relatively small proportion of global HFC usage. Globally HFC-134a makes up the major proportion of MDI manufacture (~9,500 tonnes in 2015), with HFC-227ea accounting for about 7 % (~760 tonnes in 2015). This corresponds to direct emissions with a climate impact of approximately 15 million tonnes CO2– equivalent, which is about 3 per cent of global GWP-weighted emissions of HFCs used as ODS replacements in 2014. HFC emissions from MDIs are estimated as about 0.03 per cent of annual global greenhouse gas emissions.

Environmental effect

Based on carbon footprint estimates, the estimated carbon dioxide equivalent of a 2-puff dose of an HFC MDI (200g CO2eq.) is comparable to the climate impact of everyday items, such as a 330ml can of Cola (170g CO2eq.)


Rough estimates of carbon footprints of the manufacture and use of respiratory devices were provided by IPAC. Based on a 200-dose equivalence, the estimated carbon footprint of an CFC MDI is 150-200 kg CO2eq., compared to 60-80 kgCO2eq. (HFC-227ea MDI), 20-30 kgCO2eq. (HFC-134a MDI), and 1.5‑6.0 kgCO2eq. for a DPI.


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