Determination of physical and chemical stability in pressurised metered dose inhalers: potential new techniques

Jesslynn Ooi, Daniela Traini, Ben J. Boyd, Simon Gaisford, Paul M. Young*

*Corresponding author for this work

Research output: Contribution to journalReview articlepeer-review

4 Citations (Scopus)


Introduction: Pressurised metered dose inhalers (pMDIs) are subject to rigorous physical and chemical stability tests during formulation. Due to the time and cost associated with product development studies, there is a need for online techniques to fast screen new formulations in terms of physical and chemical (physico-chemical) stability. The problem with achieving this is that pMDIs are by their definition, pressurised, making the direct observation of physico-chemical properties in situ difficult.Areas covered: This review highlights the characterisation tools that can enhance the product development process for pMDIs. Techniques investigated include: laser diffraction, Raman spectroscopy, isothermal ampoule calorimetry, titration calorimetry and gas perfusion calorimetry. The operational principles behind each technique are discussed and complemented with examples from the literature.Expert opinion: Laser diffraction is well placed to analyse real-time physical stability as a function of particle size; however, its use is restricted to suspension pMDIs. Raman spectroscopy can be potentially used to attain both suspension and solution pMDI spectra in real time; however, the majority of experiments are ex-valve chemical composition mapping. Calorimetry is an effective technique in capturing both chemical and physical degradations of APIs in real time but requires redevelopment to withstand pressure for the purposes of pMDI screening.

Original languageEnglish
Pages (from-to)1661-1675
Number of pages15
JournalExpert Opinion on Drug Delivery
Issue number10
Publication statusPublished - 3 Oct 2015
Externally publishedYes


  • drug stability
  • fast screening techniques
  • isothermal calorimetry
  • laser diffraction
  • pressurised metered dose inhalers
  • Raman


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