Indices for the brittleness of pharmaceutical tablets: a reassessment.

Brittleness is an important mechanical property. In the classical sense, a material is considered brittle if, during loading, it behaves elastically until failure. Nevertheless, it is also sometimes understood as the fact to be resistant to breakage. In the case of pharmaceutical tablets, three different indices have been defined to measure brittleness: the brittle fracture index (BFI), the brittle/ductile index (BDI) and the tablet brittleness index (TBI). The aim of this work was to reassess the meaning of the different indices that are known to give contradictory results. Using theoretical considerations, numerical modelling and experiments, it was possible to show that the only index that unequivocally measures the brittleness of the tablet understood as elastic until failure is the BFI. If the other two indices can be useful, for example to assess the friability of the tablet in the case of the TBI, they do not make it possible to measure tablet brittleness in the classical sense, i.e. as opposed to ductility.