Plasticization of a stiff pharmaceutical solid for better tabletability via cocrystallization: Shape synthons as supramolecular protecting groups

Extremely high particle stiffness and very low hardness is a serious concern in various mechanical processes in pharmaceutical manufacturing. Here we report an exceptionally high Young’s modulus (E) of ∼ 18 GPa in a drug, isoniazid (INH). This is one of the highest experimentally determined values among all reported pharmaceutical molecular crystals, which we attribute to the presence of a strong three-dimensional (3D) hydrogen bonding network (HBN). Further, we successfully reduced the 3D HBN in INH to 2D in its cocrystal using a co-former, 3,4-dimethylbenzoic acid (DMBA), where its two hydrophobic groups act like protecting groups at supramolecular level and prevent the extension of HBN. This reduced the E in the 1:1 cocrystal, INH-DMBA, by many folds and markedly improved its powder tabletability. To the best of our knowledge, this is the first reliable molecular level approach to alter the stiffness of pharmaceutical crystals and tabletability improvement in a predictable manner, hence, is important in the context of crystal engineering.