A new method to determine discoloration kinetics of uncoated white tablets occurring during stability testing-an application of instrumental color measurement in the development pharmaceutics.

The tristimulus color coordinates CIELAB and associated parameter Color Intensity (CI) have been shown to be a quantifiable variable for whiteness of uncoated tablets. Whereas any of L*, a* or b* indicates the discoloration of white tablets to a certain degree, it alone cannot reflect the full extent of discoloration. The CI has been defined which is able to describe the discoloration kinetics with acceptable regression coefficients. The evaluation of the CIELAB values from the stability data has shown that the discoloration of the white tablets means an intensification of yellowish or brownish color which is manifested by more or less constant hue angle (hab) values and increasing chroma (Cab*) values. In the view of these data the discoloration kinetics can physically be expressed by the CI. With the CI values the discoloration kinetics can be calculated by linear or polynomial regression with acceptable confidence intervals. The discoloration rates determined under several storage temperatures follow the Arrhenius equation and the activation energy can be estimated for the products. The CI values are unambiguously connected to the visual perception of the corresponding tablets. By means of the discoloration kinetics based on the CI values, it has become possible to statistically determine, the period of time uncoated tablets remain white.