The challenge of reformulation.

All current metered dose inhalers (MDIs) contain chlorofluorocarbons (CFCs) as the propellant. Two alternative hydrofluoroalkane propellants, HFA134a (tetrafluoroethane) and HFA227 (heptafluoropropane), are being investigated. The replacement of CFCs by HFAs has a major impact on all aspects of the MDI from the basic formulation to the tests required to assess performance. All commonly used surfactants are essentially insoluble in the HFA propellants. The performance of the metering valve is critical to reproducible delivery of drug from an MDI. However, the properties of the two HFA propellants are so different from CFCs that new elastomeric seals have had to be developed. The current CFC11 propellant, which is a liquid at low room temperatures, allows the drug to be introduced into the MDI as a liquid suspension before the metering valve is sealed to the canister. Both HFAs are gases at normal temperature and atmospheric pressure, therefore all handling as a liquefied propellant must be performed under high pressure in totally sealed systems. To ensure adequate performance of non-CFC MDIs new tests and standards have been developed and introduced. The development of non-CFC MDIs represents a challenging task to provide new, safe and efficacious MDI products with the minimum environmental impact.