title: Evaluation of coating properties of enteric-coated tablets using terahertz pulsed imaging.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Pharmaceutical Technology R&D Laboratories; CMC Center, Takeda Pharmaceutical Company Ltd., 2-17-85 Jusohonmachi, Yodogawa-ku, Osaka, 532-8686, Japan, masahiro.niwa@takeda.com.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Niwa
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Hiraishi
authors.forename: Katsuhide
authors.initials: K
authors.lastname: Terada
mesh_terms: D002626:Chemistry, Pharmaceutical / Q000379:methods*; D004353:Drug Evaluation, Preclinical / Q000379:methods; D013608:Tablets, Enteric-Coated / Q000737:chemistry*; D055069:Terahertz Imaging / Q000379:methods*
chemical_list: D013608:Tablets, Enteric-Coated