Diamonds in the rough: Protein crystals from a formulation perspective

The focus of the present review is to address the use of protein crystals in formulation design. Although this idea has been present for some time, i.e., insulin crystals were first reported back in 1920s, macromolecular crystallization has not received as much attention as the other methods for stabilizing protein drug candidates. The prospective potential of crystalline protein formulations in light of new advances in the field of macromolecular crystallization was reviewed, and the basic concepts and the tools now available for developing protein crystals into drug formulations are introduced. In addition, formulation challenges and regulatory demands, along with examples of current applications of protein crystals, are presented.