When formulated as liquid dosage forms, therapeutic proteins often show instability during handling as a result of chemical degradation. Solid formulations are frequently required to maintain protein stability during storage, transport and upon administration. Herein we highlight current strategies that have been developed to formulate pharmaceutical proteins in the solid form. An overview of the physical instabilities which can arise with proteins is first described. The mechanism, challenges

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... nd applications of the key solidification techniques of crystallisation, freeze-drying and particle forming technologies are subsequently discussed. Examples of current commercial products are provided to give an insight into the medical applications of this science: these include NPH-insulin crystal suspensions, freezedried monoclonal antibodies and leuproride polylactide-co-glycolide microparticles. Finally, future perspectives in solid state protein formulation are described.