Purpose: The aim of this study was to establish the suitability of terahertz (THz) transmission measurements to accurately measure and predict the critical quality attributes of disintegration time and the amount of active pharmaceutical ingredient (API) dissolved after 15, 20 and 25 min for commercial tablets processed at production scale. Methods: Samples of 18 batches of biconvex tablets from a production-scale design of experiments study into exploring the design space of a commercial tablet manufacturing process were used. The tablet production involved the process steps of high-shear wet granulation, fluid-bed drying and subsequent compaction. The 18 batches were produced using a 4 factor split plot design to study the effects of process changes on the disintegration time. Non-destructive and contactless terahertz transmission measurements of the whole tablets without prior sample preparation were performed to measure the effective refractive index and absorption coefficient of 6 tablets per batch. Results: The disintegration time (R2 = 0.86) and API dissolved after 15 min (R2 = 0.96) linearly correlates with the effective refractive index, neff, measured at terahertz frequencies. In contrast, no such correlation could be established from conventional hardness measurements. The magnitude of neff represents the optical density of the sample and thus it reflects both changes in tablet porosity as well as granule density. For the absorption coefficient, αeff, we observed a better correlation with dissolution after 20 min (R2 = 0.96) and a weaker correlation with disintegration (R2 = 0.83) compared to neff. Conclusion: The measurements of neff and αeff provide promising predictors for the disintegration and dissolution time of tablets. The high penetration power of terahertz radiation makes it possible to sample a significant volume proportion of a tablet without any prior sample preparation. Together with the short measurement time (seconds), the potential to measure content uniformity and the fact that the method requires no chemometric models this technology shows clear promise to be established as a process analyser to non-destructively predict critical quality attributes of tablets.
- disintegration time
- refractive index