Novel insights into controlled drug release from coated pellets by confocal Raman microscopy

The development of novel therapeutics with improved efficacy implies increasing complexity of drug delivery systems, which in turn require advanced methods for their analytical characterization. Among these systems, pellets represent upcoming carrier systems, which show several advantages like simplified dosing and improved compliance among children and the aged population. However, rational development of such systems is hampered by the lack of non‐destructive, chemically selective analytical insight into compound distribution and drug release mechanisms. The aim of this study was to evaluate confocal Raman microscopy (CRM) for investigation of coated drug‐loaded pellets based on visualization of compound distribution and elucidation of drug release mechanisms. Three complementary approaches were applied for pellet characterization: analysis of cross sections after bisectioning, non‐invasive visualization of the pellet surface, and virtual cross sectioning in x–z direction. As the surface of such pellets is structured, a complementary approach of optical topography and CRM was applied for three‐dimensional analysis. Based on the individual Raman peak patterns, the drug and excipients forming the matrix of the pellets and the film coating were successfully visualized with high spatial resolution, verifying homogeneous drug distribution and intact polymer coating of the pellet. Further, analysis of the pellets after certain time intervals during drug release testing revealed pore formation in the polymer coating facilitating drug release and preceding drug depletion in the pellets matrix. CRM represents an upcoming technique for analytical characterization of carrier systems and elucidation of their complex drug release mechanisms, thus supporting rational development of novel therapeutics. Copyright © 2016 John Wiley & Sons, Ltd.