Color is a very important characteristic of film coated tablets. It ensures easier recognition, harder forgery and it often leads to better patient compliance. Developing a product, an obstacle is often encountered, in how to reliably reproduce the desired shade of color. The desired coloring of a film coated tablet is achieved by using an abundance of pigments. In recent years, though, this is becoming increasingly more difficult due to new toxicological studies suggesting some of those pigments are unsafe. In this Master’s thesis, the preparation of film coatings of different colors, using following pigments: red, yellow and black iron oxide and indigo carmine was studied. Using design of experiments methodology, 2 models were set up for color parameter prediction in the CIEL*a*b* color space. The yellow-red model predicts the color while using a white base (including the polymer, plasticizer, lubricant and titanium dioxide) plus the yellow or red iron oxide pigment; while the comprehensive model additionally includes the rest of the pigments: black iron oxide and indigo carmine. Building these models, it was successfully shown that design of experiments methodology can be used to predict color parameters, providing the number of experiments is large enough.
Additionally, the models were tested for their use in the reverse fashion as well, meaning predicting pigment composition from data of a certain targeted color. The color of reference tablets was measured and the designed model then used to predict the optimal composition of pigments to achieve the desired color of film coated tablets. The yellow-red model fared well in this test, successfully predicting the optimal pigment composition. The analytical descriptiors of reference tablets and tablets produced by the results of this model were virtually identical. The comprehensive model proved less reliable in this fashion and did not predict the pigment composition correctly. Suggesting the comprehensive model requires a larger data set.
Further, additional hypotheses that relate to usefulness of these models were tested. For example, the reproducibility of film coating in terms of the color, the impact of changes in the relief of tablet cores and various coloring of the tablet core on the color of film coated tablets. The impact on the color of film coated tablets when switching the polymer was also checked. To optimize the process of film coating time-wise, it was additionally tested how the color of the tablets and the evenness of coloring changes during the process of film coating.
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