Component crystallization and physical collapse during freeze-drying of aqueous solutions containing protein-stabilizing L-arginine and citric acid mixtures were studied. Freeze-drying microscopy (FDM) and thermal analysis of the solute-mixture frozen solutions showed collapse onset at temperatures (T c ) approximately 10°C higher than their T g ′s (glass transition temperatures of the maximally freeze-concentrated solute phase). Experimental freeze-drying of these solutions at a low chamber pressure showed the occurrence of physical collapse at shelf temperatures close to or slightly higher than the T c . Slower ice sublimation at higher chamber pressures induced the physical collapse from lower shelf temperatures. The large effect of chamber pressures on the collapse-inducing shelf temperatures confirmed significance of the sublimation-related heat loss on the sublimation interface temperature during the primary drying. Drying of the single-solute L-arginine solution resulted in cake-structure solids composed of its anhydrous crystal. Thermal and powder X-ray diffraction (PXRD) analysis suggested slow crystal nucleation of L-arginine dihydrate in the frozen solutions. Characterization of the frozen solutions and freeze-dried solids should enable rational formulation design and process control of amino acid-containing lyophilized pharmaceuticals.Key words freeze-drying; crystallization; glass; lyophilization; collapse; thermal analysis Clinical applications of protein pharmaceuticals such as therapeutic antibodies are increasing. However, marginal storage stabilities of many proteins in the aqueous solutions emphasize the importance of developing freeze-dried formulations. Many lyophilized protein formulations contain disaccharides (e.g., sucrose and trehalose) that protect the proteins thermodynamically from structural changes during the freeze-drying process and kinetically from chemical degradation during subsequent storage.1,2) Some basic amino acid (e.g., L-arginine and L-histidine) and multivalent acid (e.g., H 3 PO 4 and citric acid) mixtures are practical alternative stabilizers for protein formulations.3-6) The mixtures protect proteins from conformation-altering dehydration stress during the process. These mixtures form glass-state amorphous solids through networks of hetero-component molecular interactions between the amino and carboxyl groups, and thus improve chemical stability of the dried proteins during storage. 5,7)L-Arginine also increases solubility of various proteins without apparent changes in their conformation. [8][9][10] Freeze-drying is a typical high-energy process, and varying its parameters significantly varies the formulation quality, including the cake appearance, component crystallinity, residual water, and stability of the active pharmaceutical ingredients (APIs).11,12) Failure of a biopharmaceutical lyophilization batch would lead to the loss of the therapeutic protein often more expensive than small molecular APIs. Freezing of aqueous solutions concentrates most solutes to a s...

No abstract