Pharmaceutical Research

, Volume 31, Issue 8, pp 2140–2151 | Cite as

Evaluation of Coating Properties of Enteric-Coated Tablets Using Terahertz Pulsed Imaging

Research Paper



Enteric coatings are used to reduce gastrointestinal side effects and control the release properties of oral medications. Although widely used, the effect of formulation and process conditions on physicochemical and functional properties of enteric coatings remains unclear.


Terahertz pulsed imaging (TPI) was employed to evaluate the coat properties of enteric coated tablets (ECTs) with various acid resistance. Other analytic methods, such as loss on drying, scanning electron microscopy and X-ray computed tomography were then used to validate the relationships established among 4 TPI-derived parameters and the physicochemical properties of enteric coatings.


Weight gain measurement did not provide any information to assess acid resistance of enteric coating, whereas four TPI-derived parameters non-destructively reflected the coating properties such as thickness, coat uniformity, density, and water distribution, allowing the identification of the causes of poor acid resistance in certain ECT batches using a single measurement. These parameters also revealed the effect of coating conditions; in particular, coating under dry conditions led to less dense and nonuniform coatings with poor acid resistance.


We demonstrated the utility of TPI to identify structural defects within ECTs with poor acid resistance. TPI-derived parameters can aid in formulation development and quality control of ECTs.


acid uptake coating uniformity enteric coated tablets terahertz pulsed imaging X-ray CT scan 



Analysis of variance


Active pharmaceutical ingredient


Enteric coated tablet


Loss on drying


Minimum film forming temperature


Near infrared spectroscopy


Scanning electron microscopy


Terahertz electric field peak strength


Terahertz pulsed imaging


X-ray computed tomography



The authors would like to acknowledge the help of Muneo Nonomura and Ayako Baba in Takeda, Tsuyoshi Miura from Bruker Optics, Jesse Alton and Philip F Taday from Teraview for their valuable suggestions and assistance with this study, which has been a great aid toward the publication of this paper.


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Copyright information

© Springer Science+Business Media New York 2014

Authors and Affiliations

  1. 1.Pharmaceutical Technology R&D Laboratories; CMC CenterTakeda Pharmaceutical Company Ltd.OsakaJapan
  2. 2.Faculty of Pharmaceutical SciencesToho UniversityFunabashiJapan

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