Incorporation of an active pharmaceutical ingredient (API) into the coating layer of film-coated tablets is a method mainly used to formulate combination tablets. Uniform and precise spray coating of an API represents, however, a substantial challenge that could be overcome by applying Raman spectroscopy as process analytical tool. In the present work, active-coating experiments for osmotic-controlled-release oral delivery system (OROS) tablets were performed in a side-vented lab-scale pan coater. During the process, Raman spectra were recorded in-line and off-line after sampling. Quantitative multivariate calibration models were built up by correlating these spectra with the coated API amount at each sampling point. Three different modeling approaches were tested on a second batch with regard to their predictive ability and robustness. By applying the in-line model development approach on OROS tablets, it was possible to overcome the difficulties of this dosage form with each layer contributing differently to the resulting spectroscopic signal and to determine accurately the applied API amount on two-layer tablets. Thereby, the present study demonstrated that Raman spectroscopy can be successfully implemented as a process analytical technology tool to control and monitor an active-coating process of OROS tablets.
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