title: Terahertz pulsed imaging as an advanced characterisation tool for film coatings--a review.
abstract: Solid dosage forms are the pharmaceutical drug delivery systems of choice for oral drug delivery. These solid dosage forms are often coated to modify the physico-chemical properties of the active pharmaceutical ingredients (APIs), in particular to alter release kinetics. Since the product performance of coated dosage forms is a function of their critical coating attributes, including coating thickness, uniformity, and density, more advanced quality control techniques than weight gain are required. A recently introduced non-destructive method to quantitatively characterise coating quality is terahertz pulsed imaging (TPI). The ability of terahertz radiation to penetrate many pharmaceutical materials enables structural features of coated solid dosage forms to be probed at depth, which is not readily achievable with other established imaging techniques, e.g. near-infrared (NIR) and Raman spectroscopy. In this review TPI is introduced and various applications of the technique in pharmaceutical coating analysis are discussed. These include evaluation of coating thickness, uniformity, surface morphology, density, defects and buried structures as well as correlation between TPI measurements and drug release performance, coating process monitoring and scale up. Furthermore, challenges and limitations of the technique are discussed.
authors.affiliation: School of Pharmacy, University of Otago, P.O. Box 56, Dunedin, New Zealand; Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, UK; TeraView Ltd., St. John's Innovation Park, Cambridge CB4 0WS, UK.
authors.forename: Miriam
authors.initials: M
authors.lastname: Haaser
authors.forename: Keith C
authors.initials: KC
authors.lastname: Gordon
authors.forename: Clare J
authors.initials: CJ
authors.lastname: Strachan
authors.forename: Thomas
authors.initials: T
authors.lastname: Rades
mesh_terms: D004364:Pharmaceutical Preparations / Q000737:chemistry*; D011786:Quality Control; D013499:Surface Properties; D013678:Technology, Pharmaceutical / Q000379:methods*; D055069:Terahertz Imaging
chemical_list: D004364:Pharmaceutical Preparations
keywords: Controlled release; Film coating; Imaging analysis; Solid dosage forms; Terahertz pulsed imaging (TPI)