Reconstitution Time for Highly Concentrated Lyophilized Proteins: Role of Formulation and Protein

Lyophilized protein formulations containing highly concentrated proteins often have long reconstitution times. The goal was to understand the role of formulation in mediating the reconstitution time. Formulation variables such as % total solids, protein concentration, protein-to-sugar ratio, different proteins and inclusion of a crystallizable excipient were investigated for their effect on cake properties influencing reconstitution namely, cake wettability, penetration of reconstitution fluid into the cake, cake disintegration and cake porous structure. Additionally, several measures of viscosity were also evaluated for their effect on reconstitution time. Reconstitution time was primarily influenced by the "concentrated formulation viscosity" with negligible contributions from % total solids and protein concentration. "Concentrated formulation viscosity" was sensitive to both protein-to-sugar ratio and the protein itself. Partial crystallinity in the final cake also expedited reconstitution. Wettability, liquid penetration into the cake, cake disintegration tendency and cake porous structure were found to be invariant for amorphous cakes and did not correlate with reconstitution time. However, these properties were sensitive to the presence of crystallinity and resulted in faster reconstitution at least of the partially crystalline cakes. "Concentrated formulation viscosity" strongly correlated with reconstitution times of amorphous cakes, providing insights on the steps involved in the reconstitution of amorphous formulations.