Screening of novel excipients for freeze-dried protein formulations.

The typical excipients used as bulking agents and lyoprotectants for freeze-drying are usually limited to only a few selected substances, such as sucrose and mannitol. Considering the sheer diversity amongst proteins, it is doubtful that this limited choice should, in every case, provide the best possible option in order to achieve the most stable product. In this work, a screening of 12 proteins with 64 excipients was conducted in order to increase the knowledge space of potential excipients. Three critical quality attributes (CQAs) of the freeze-dried products, namely the solid state, the cake appearance and the protein integrity based on changes in tryptophan fluorescence were investigated by high throughput X-ray powder diffraction, image analysis and intrinsic fluorescence spectroscopy, respectively. It was found, that in some cases the excipient had a dominating influence on the CQAs, whilst in other cases the CQAs were primarily protein dependent, or that the CQAs were dependent on the combination of both. In the course of this investigation, a general view of potentially relevant excipients, and their interplay with various proteins, was obtained, thereby furthermore paving the way for the use of novel freeze-drying excipients.