Purpose: The stabilizing effect of amphiphilic excipients and sugars against protein inactivation during freeze-drying was studied in relation to their physical states in freeze-dried cakes.
Methods: Physical states of amphiphilic excipients were studied by powder X-ray diffractometry and differential scanning calorimetry (DSC). Stabilizing effects of excipients were studied using lactate dehydrogenase (LDH) as a model protein.
Results: Although poly(ethylene glycols) (PEGs) 1000 to 2000 crystallized when freeze-dried alone, the addition of sugars decreased their crystallinity by dispersing PEG into sugar-dominant matrices. Sugars species, molecular weight of PEGs, and buffer concentration also affected the crystallinity of PEGs. Sugars also dispersed some of other amphiphilic excipients, which tended to crystallize or become "microscopically liquid" when freeze-dried without sugar. Only the amphiphilic excipients that remained amorphous solid state protected the enzyme during freeze-drying in the absence of sugars. However, combinations of sucrose and all the amphiphilic excipients studied increased the stabilizing effects markedly. The remaining activities were greater than the sum of their individual ones.
Conclusions: Various amphiphilic excipients are good stabilizers for freeze-drying of proteins when dispersed into sugar-dominant matrices.