Optics-based compressibility parameter for pharmaceutical tablets obtained with the aid of the terahertz refractive index

Mousumi Chakraborty, Cathy Ridgway, Prince Bawuah, Daniel Markl, Patrick A.C. Gane, Jarkko Ketolainen, J. Axel Zeitler, Kai Erik Peiponen

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The objective of this study is to propose a novel optical compressibility parameter for porous pharmaceutical tablets. This parameter is defined with the aid of the effective refractive index of a tablet that is obtained from non-destructive and contactless terahertz (THz) time-delay transmission measurement. The optical compressibility parameter of two training sets of pharmaceutical tablets with a priori known porosity and mass fraction of a drug was investigated. Both pharmaceutical sets were compressed with one of the most commonly used excipients, namely microcrystalline cellulose (MCC) and drug Indomethacin. The optical compressibility clearly correlates with the skeletal bulk modulus determined by mercury porosimetry and the recently proposed terahertz lumped structural parameter calculated from terahertz measurements. This lumped structural parameter can be used to analyse the pattern of arrangement of excipient and drug particles in porous pharmaceutical tablets. Therefore, we propose that the optical compressibility can serve as a quality parameter of a pharmaceutical tablet corresponding with the skeletal bulk modulus of the porous tablet, which is related to structural arrangement of the powder particles in the tablet.

Original languageEnglish
Pages (from-to)85-91
Number of pages7
JournalInternational Journal of Pharmaceutics
Issue number1
Early online date2 Apr 2017
Publication statusPublished - 15 Jun 2017


  • indomethacin
  • microcrystalline cellulose
  • optical compressibility
  • pharmaceutical tablet
  • skeletal bulk modulus
  • structural parameter
  • terahertz

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