Main applications

Medical aerosol applications have these requirements, which was provided traditionnaly by the CFCs, progressively replaced by HCFs, the only propellants that can meet the need of non-flammability, while being virtually non-toxic.

These aerosol products are extremely important e.g. Metered Dose Inhalers (MDIs) for therapy of asthma and other respiratory problems. MDIs prove to be a very effective means of administering the active drug, are cost effective and particularly suitable for use by children and the elderly. Propellants of proven very low toxicity must be used for this application.

Medical aerosols are essential for patients health, and as much must be distinguishead from industrial aerosols.

The HFCs 134a and 227ea (both pharma grade) are used as propellants for metered dose inhalers (MDIs) for the treatment of asthma and chronic obstructive pulmonary diseases (COPD).
There is international consensus that primary treatment of these diseases should be via inhalation, with the MDI remaining the dominant inhaled delivery system in most countries and for all categories of drugs.

The incidence of asthma and COPD in developed countries is around 5 to 8 % of the population and increasing at an average rate of around 5 % per year.
These diseases are particularly prevelant amongst children, as the incidence in this group now approaches 15 % in Western Europe.

Worldwide at least 300 million people suffer from asthma, and a comparable number from COPD. A minimum of 50 to 60 million patients therefore rely on metered dose inhalers.

Technical and safety aspects

Technical

HFCs used for medical aerosols :
Asthma often occurs in the form of life-threatening, acute attacks which need immediate treatment. Therefore, patients always have to carry with them the necessary active substance in small pocket-sized dispensers, the metered dose inhalers. The dispenser contains a mixture consisting of the propellant and the pharmaceutical active substance dissolved or suspended in the liquified propellant and sometimes with further excipients such as co-solvents and/or surfactants added in very small amounts. This couple formulation dictates the choice between HFC-134a and HFC227ea, based on their different physico-chemical properties.
When the patient actuates the MDI, the propellant immediately evaporates at ambient conditions and produces a fine spray, the aerosol, which directly has to be inhaled via the mouthpiece.

Safety aspects

Both HFC 134a and HFC 227ea were extensively tested by the International Pharmaceutical Aerosol Consortium for Toxicity Testing and were found to be toxicologically safe. Together with their chemical inertness and non-flammability they offer the degree of safety indispensable for this medical application.

Recovery and recycling

In the MDI production process there is always a certain fraction of products that fail to meet the quality standards and are rejected during the quality control process. It is possible to remove the HFCs in these MDIs to recycle or safely destroy them in order to prevent their release into the atmosphere.

Measures to implement such recovery techniques at MDI manufacturing sites in the EU are currently in consideration respectively under development. Propellant recovery systems, once established, could also be applied for used MDIs which are still not completely empty.

Economic aspects

The MDI delivery system represents about 85 % of the relevant drug application in the EU and about 90 % worldwide. The main barriers for alternative delivery systems like dry powder inhalers (DPIs) are cost and usability (acceptance by patients). Typically the cost for a DPI is 2 1/2 fold compared to the cost for the corresponding MDI.

It is expected that by 2005 all drugs delivered by MDIs today will be available with HFC propellant in the EU. This ongoing transition from CFCs (chlorofluorocarbons) to HFCs (hydrofluorocarbons) as MDI propellants will reduce the global warming impact of MDI emissions by at least 75 % from 2000 to 2010.

In a business-as-usual scenario MDI emissions in the EU in 2010 are predicted to 5 to 6 Mtonnes CO₂ equivalents corresponding to 0.13 % of total emissions, compared to a contribution of 1 % in 1995.