While the albuterol market, which is worth around $400m according to a 2007 report by decision resources, represents a considerable opportunity, generics firms have been slow to develop HFA products.
Observers have commented that this is due to some of the expensive technical challenges that need to be overcome.
A 2005 research paper, "The CFC to HFA transition and its impact on pulmonary drug development" by Dr Chet Leach of the Lovelace Respiratory Research Institute, discussed some of these challenges.
He explained that problems ranging from the poor compatibility of surfactants with HFA to difficulties associated with sealant technologies have hampered development efforts.
Dr Leach added that because the thermodynamic properties of CFCs and HFAs differ considerably, the design of the inhaler, known as the boot, is critical in ensuring both the correct particle diameter and size and shape of the delivery plume.
He also said that manufacturing facilities need significant modification to be capable of safely producing HFA-based inhalers, particularly as a result of the use of flammable co-solvents such as ethanol.
Only branded HFA albuterols approved At present, only three branded HFA albuterol products are approved by the Food and Drug Administration (FDA): Teva's Proair HFA; Schering Plough's Proventil HFA; and GlaxoSmithKline's Ventolin HFA.
CFC-propelled generic albuterols make up around 35 per cent of the total market.
According to Reuters, Boston-based aerosols specialist Armstrong Pharmaceuticals, which is the only firm to manufacturer CFC-based albuterols, plans to halt production ahead of the December 31 deadline.
In a study published last year, Datamonitor predicted that the ban will shift the albuterol market considerably.
They forecast that Teva's ProAir was most likely to reap the benefits due to its favourable price compared with other HFA products.
The US government's move is in keeping with its commitment to the 1987 Montreal protocol, which was designed to limit the use of substances that deplete the ozone layer.
Additionally, the ban is covered by the country's more recent clean air legislation.
Jane Woodcock, director of the Food and Drug Administration's (FDA) Center for Drug Evaluation and Research explained that "concern about the environment stimulated the need to phase out CFCs ."
Woodcock added that the agency is keen emphasize that the products " are safe and effective replacements for CFC-propelled albuterol inhalers."
Propellant switch technically challenging While the replacement of a propellant that damages the environment for one that does not is conceptually simple, pharmaceutical firms have had to invest millions of dollars in developing new technologies to facilitate the change.
With regard to the wider $7bn inhaler market, Dr Leach added that while the number of patents for new inhaler technologies rose from around 5 per year in the1980s to approximately 350 a year through the1990s, the price advantages offered by MDIs will probably allow them to maintain their dominance of the market.