Abstract
Tablet dissolution is strongly affected by swelling and solvent penetration into its matrix. A terahertz-pulsed imaging (TPI) technique, in reflection mode, is introduced as a new tool to measure one-dimensional swelling and solvent ingress in flat-faced pharmaceutical compacts exposed to dissolution medium from one face of the tablet. The technique was demonstrated on three tableting excipients: hydroxypropylmethyl cellulose (HPMC), Eudragit RSPO, and lactose. Upon contact with water, HPMC initially shrinks to up to 13% of its original thickness before undergoing expansion. HPMC and lactose were shown to expand to up to 20% and 47% of their original size in 24 h and 13 min, respectively, whereas Eudragit does not undergo dimensional change. The TPI technique was used to measure the ingress of water into HPMC tablets over a period of 24 h and it was observed that water penetrates into the tablet by anomalous diffusion. X-ray microtomography was used to measure tablet porosity alongside helium pycnometry and was linked to the results obtained by TPI. Our results highlight a new application area of TPI in the pharmaceutical sciences that could be of interest in the development and quality testing of advanced drug delivery systems as well as immediate release formulations. © 2015 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 104:1658–1667, 2015
Highlights
Solid dosage forms are used to deliver active pharmaceutical ingredients (APIs) to treat a range of conditions, and advanced drug delivery formulations can be used to adjust the drug release over short, long, or sustained periods of time at a specified rate
MATERIALS AND METHOD Materials The samples were powder compacts of hydroxypropylmethyl cellulose (HPMC) (K15m; ColorChem, Atlanta, Georgia), one of the most widely used commercial swelling hydrophilic polymers used for sustained drug release formulations[34]; Eudragit RSPO (Evonik, Hamburg, Germany), which forms nonswelling matrices that can be used as a tablet matrix for sustained drug release; and lactose "-monohydrate (Meggle, Wasserburg, Germany), which is a soluble, filler, diluent, and bulking agent commonly found in immediate-release formulations
We have demonstrated that terahertz imaging can be used as a powerful tool to investigate diffusion within pharmaceutical powder compacts
Summary
Solid dosage forms are used to deliver active pharmaceutical ingredients (APIs) to treat a range of conditions, and advanced drug delivery formulations can be used to adjust the drug release over short, long, or sustained periods of time at a specified rate. For a range of matrix formulations, it has been demonstrated that the interaction of the tablet with its surroundings can be described by the so-called shrinking core mechanism and variants thereof.[2] The shrinking core mechanism model describes diffusion-controlled processes such as the interaction of the dissolution medium with the solid and its ensuing physical conversions. This process is described to occur layer by layer until the drug release is complete,[2] and it provides very good estimates for some formulations, it is not suited for all formulations.
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