Crystal Engineering of Pharmaceutical Cocrystals

In the last years, the design and synthesis of co-crystals containing active pharmaceutical ingredients (APIs) has become the new frontier of the crystal engineering due to the great opportunity to modify the physico-chemical properties of solid forms of drugs. Actually, the pharmaceutical co-crystals display intermolecular motifs and hence crystal structure different from the pure API component, and consequently can exhibit diverse specific physical properties, such as solubility and dissolution rate; this makes it possible to hypothesize interesting influences in the bioavailability or local delivery of the drug itself. An efficient preparation of desired cocrystals requires an understanding and exploitation of the intermolecular interactions which may occur between the API and the other crystal co-formers in order to obtain robust supramolecular synthons. Relying on our long experience in the study of intermolecular interactions (in particular hydrogen bonding) and of co-crystals in general, we have started a project of supramolecular synthesis using different APIs and aromatic bases. In this communication the focus will be on cocrystals containing phloroglucinol (an example is shown in Fig.1), an antispasmodic agent, carbamazepine, an anticonvulsant, and indomethacin, a non-steroidal anti-inflammatory drug. Besides a detailed investigation of the characteristic behaviour of the coformers’ functional groups (mostly hydrogen bonding donors or acceptors) and their influence on the crystal structures and packing motifs, the solubility and dissolution rate of some indomethacin cocrystals have been evaluated.