Mannitol/sucrose formulations are employed to generate lyophilizates for biopharmaceuticals with an elegant cake appearance. The aim of this study was to dry protein/mannitol/sucrose formulations as fast as possible without loss of cake appearance and protein stability. Glycerol was included as potential additional protein stabilizer. Three proteins (lysozyme and two monoclonal antibodies) at low and high concentration were analyzed comparing fast with conservative freeze-drying.
Freeze-drying cycle development was carried out with mannitol/sucrose formulations. A product temperature (Tp) close to the Te of mannitol and clearly above the Tg’ of sucrose was targeted. Protein formulations were exposed to the final fast lyophilisation process and to a conservative freeze-drying cycle. Lyophilizates were characterized by differential scanning calorimetry, Karl-Fischer titration and X-ray diffractometry. Additionally, macroscopic cake appearance and reconstitution times were evaluated. Protein stability was characterized by UV/Vis spectroscopy, light obscuration and size exclusion chromatography.
The fast freeze-drying cycle resulted in a primary drying time of 7 hours (Tp: –10 °C) and a secondary drying time of 2 hours in contrast to 47 hours (Tp: –39 °C) and 12 hours for the conservative cycle. Lyophilizates showed Tg values above 60 °C, a residual moisture level of 1%, reconstitution times of less than 35 seconds, δ-mannitol and elegant cake appearance. Mannitol/sucrose ratios below 4/1 did not lead to complete mannitol crystallization and were therefore not suitable for the selected process conditions. Characterisation of protein stability rendered low aggregation and particle levels for both, fast and conservative freeze-drying conditions.
It was shown that fast freeze-drying of mannitol/sucrose formulations above Tg’ at a Tp of –10 °C resulted in good protein process stability and appropriate cake characteristics at maximum time reduction.