Addition of Amino Acids to Further Stabilize Lyophilized Sucrose-Based Protein Formulations: I. Screening of 15 Amino Acids in Two Model Proteins.

In small amounts, the low molecular weight excipients-sorbitol and glycerol-have been shown to stabilize lyophilized sucrose-based protein formulations. The purpose of this study was to explore the use of amino acids as low molecular weight excipients to similarly enhance stability. Model proteins, recombinant human serum albumin and α-chymotrypsin, were formulated with sucrose in combination with one of 15 amino acid additives. Each formulation was lyophilized at 1:1:0.3 (w/w) protein-sucrose-amino acid. Percent total soluble aggregate was measured by size-exclusion chromatography before and after storage at 50 °C for 2 months. Classical thought might suggest that the addition of the amino acids to the sucrose-protein formulations would be destabilizing because of a decrease in the system's glass transition temperature. However, significant improvement in storage stability was observed for almost all formulations at the ratio of amino acid used. Weak correlations were found between the extent of stabilization and both amino acid molar volume and side-chain charge. The addition of amino acids at a modest level generally improves storage stability, often by more than a 50% increase, for lyophilized sucrose-based protein formulations.

Addition of Monovalent Electrolytes to Improve Storage Stability of Freeze-Dried Protein Formulations.

This study investigates the effect of low levels of electrolytes on storage stability in freeze-dried sucrose-based protein formulations. Both bovine serum albumin and recombinant human serum albumin were freeze dried with sucrose and alkali halides (LiCl, NaCl, KCl, RbCl, and CsCl) at selected low levels. All formulations were stored at 50 °C and 65 °C up to 2 months and then assayed for protein aggregation. The data demonstrate that low levels of LiCl and NaCl enhance stability. No obvious correlations with either protein secondary structure or global dynamics (structural relaxation time) were found. However, good correlations were found between stability and both free-volume hole size via positron annihilation lifetime spectroscopy (PALS) and fast dynamics by neutron scattering. Volume changes on mixing and the partial molal volume of salt were also studied in an effort to detect decreases in free volume. These data did not support the hypothesis that reduction in free volume was the primary mechanism for salt-induced stabilization. Finally, a positive effect of postlyophilization annealing on stability was demonstrated. In summary, we find that small amounts of LiCl and NaCl significantly stabilize these proteins, which is a result at variance with conventional formulation wisdom.

Mathematical Models to Explore Potential Effects of Supersaturation and Precipitation on Oral Bioavailability of Poorly Soluble Drugs.

Poorly soluble drugs are increasingly formulated into supersaturating drug delivery systems which may precipitate during oral delivery. The link between in vitro drug concentration profiles and oral bioavailability is under intense investigation. The objective of the present work was to develop closed-form analytical solutions that relate in vitro concentration profiles to the amount of drug absorbed using several alternate assumptions and only six parameters. Three parameters define the key features of the in vitro drug concentration-time profile. An additional three parameters focus on physiological parameters. Absorption models were developed based on alternate assumptions; the drug concentration in the intestinal fluid: (1) peaks at the same time and concentration as in vitro, (2) peaks at the same time as in vitro, or (3) reaches the same peak concentration as in vitro. The three assumptions provide very different calculated values of bioavailability. Using Case 2 assumptions, bioavailability enhancement was found to be less than proportional to in silico examples of dissolution enhancement. Case 3 assumptions lead to bioavailability enhancements that are more than proportional to dissolution enhancements. Using Case 1 predicts drug absorption amounts that fall in between Case 2 and 3. The equations developed based on the alternate assumptions can be used to quickly evaluate the potential improvement in bioavailability due to intentional alteration of the in vitro drug concentration vs. time curve by reformulation. These equations may be useful in making decisions as to whether reformulation is expected to provide sufficient bioavailability enhancement to justify the effort.

Optimization of a Raman microscopy technique to efficiently detect amorphous-amorphous phase separation in freeze-dried protein formulations.

A confocal Raman microscopic technique was optimized to more efficiently detect amorphous-amorphous phase separation in freeze-dried protein formulations. A Renishaw Raman inVia confocal microscope was used to collect 100-200 µm line maps (2 µm step size) of freeze-dried protein-excipient formulations. At each point across the line map, the composition was evaluated from the intensity of the nonoverlapping peaks representative of each component. Collection aperture, scan time, and line map length significantly contributed to the phase-separation analysis, whereas different sample preparation methods did not affect the analysis. Using the optimized parameters (i.e., large aperture 5 s scan time, 200 µm line map), phase separation was successfully detected in binary polymer formulations and was comparable to the previously developed Raman method. However, the previous method required 2.5 h/sample, whereas the optimized method only requires 0.5 h/sample. Phase separation was detected in the following protein-excipient formulations: lysozyme-trehalose (1:1), lysozyme-isomaltose (1:1), ß-lactoglobulin-dextran (1:1), ß-lactoglobulin-dextran (1:3), and ß-lactoglobulin-trehalose (1:1). Phase separation was not detected in lysozyme-sucrose (1:1) and ß-lactoglobulin-sucrose (1:1) formulations. The optimized method successfully detected phase separation in several protein formulations, where phase separation was previously suspected, and promised to be a useful tool for detection of phase separation in amorphous therapeutic formulations.