The official Pharmacopeia does not include a test procedure for the in vitro estimation of the chewability of tablets and publications in the scientific literature on this subject are rare. The purpose of this study was to evaluate a number of different test procedures for assessing chewability, starting from standard breaking force and strength testing and progressing to develop new procedures that simulate the actual chewing action on tablets. A further goal was to apply these test procedures to characterize the chewability of the novel phosphate binder PA21 in comparison with a commercially available phosphate binder chewable tablet product based on lanthanum (Fosrenol®) and a chewable tablet product containing calcium (Calcimagon®) - the latter being used as a standard for its very good chewability. For this purpose, a number of development formulations (different batches of PA21) were tested. The radial or diametrical tablet breaking force offers a poor means of assessing chewability while the axial breaking force was concluded to better reflect the effect of chewing on the tablet. Measurement of tablet behavior upon repeated loading afforded the best simulation of the actual chewing action and was found to have a good discriminating power with respect to chewability of the tested tablets, especially when the tablet was moistened with artificial saliva. The developed tests are shown to be more suitable for evaluating chewing properties of tablets than currently used Pharmacopeial tests. Following ICHQ6, which calls for specification of hardness for chewable tablets, these test procedures enabled the optimal chewability features of PA21 tablets in development to be confirmed whilst still maintaining capabilities for robust production and transportation processes.
Keywords: Artificial saliva; axial breaking force; chewability; chewable tablets; hyperphosphatemia; in-vitro test; indentation; radial breaking force.