Smith I J
Glaxo Research and Development Ltd, Ware, Herts, UK.
J Aerosol Med. 1995 Spring;8 Suppl 1:S19-27. doi: 10.1089/jam.1995.8.suppl_1.s-19.
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.
所有现有的定量吸入气雾剂（MDIs）都含有氯氟烃（CFCs）作为推进剂。目前正在研究两种替代的氢氟烷烃推进剂，即HFA134a（四氟乙烷）和HFA227（七氟丙烷）。用氢氟烷烃替代氯氟烃对定量吸入气雾剂从基本配方到评估性能所需的测试等各个方面都有重大影响。所有常用的表面活性剂基本上都不溶于氢氟烷烃推进剂。计量阀的性能对于从定量吸入气雾剂中可重复递送药物至关重要。然而，这两种氢氟烷烃推进剂的性质与氯氟烃有很大不同，因此必须开发新的弹性密封件。目前的CFC11推进剂在低温下是液体，在计量阀密封到药罐之前，可使药物以液体悬浮液的形式引入定量吸入气雾剂中。两种氢氟烷烃在常温常压下都是气体，因此作为液化推进剂的所有操作都必须在完全密封的系统中在高压下进行。为确保无氯氟烃定量吸入气雾剂有足够的性能，已制定并引入了新的测试和标准。开发无氯氟烃定量吸入气雾剂是一项具有挑战性的任务，要提供对环境影响最小的新型、安全且有效的定量吸入气雾剂产品。
