The role of co-crystals in pharmaceutical design

Pharmaceutical co-crystal formation represents a straightforward way to dramatically influence the solid-state properties of a drug substance, particularly its solubility and hence bioavailability. This short review summarises this highly topical field, covering why the topic is of interest in pharmaceutical formulation, the definitions and practical scope of co-crystals, co-crystal preparation and characterisation, and implications for regulatory control and intellectual property (IP) protection. Concepts are illustrated with highly selected examples of pharmaceutical co-crystal systems within the wider context of crystal engineering and research in molecular solids.