Amino Acids as Co-amorphous Excipients for Simvastatin and Glibenclamide: Physical Properties and Stability

Co-amorphous drug mixtures with low-molecular-weight excipients have recently been shown to be a promising approach for stabilization of amorphous drugs and thus to be an alternative to the traditional amorphous solid dispersion approach using polymers. However, the previous studies are limited to a few drugs and amino acids. To facilitate the rational selection of amino acids, the practical importance of the amino acid coming from the biological target site of the drug (and associated intermolecular interactions) needs to be established. In the present study, the formation of co-amorphous systems using cryomilling and combinations of two poorly water-soluble drugs (simvastatin and glibenclamide) with the amino acids aspartic acid, lysine, serine, and threonine was investigated. Solid-state characterization with X-ray powder diffraction, differential scanning calorimetry, and Fourier-transform infrared spectroscopy revealed that the 1:1 molar combinations simvastatin–lysine, glibenclamide–serine, and glibenclamide–threonine and the 1:1:1 molar combination glibenclamide–serine–threonine formed co-amorphous mixtures. These were homogeneous single-phase blends with weak intermolecular interactions in the mixtures. Interestingly, a favorable effect by the excipients on the tautomerism of amorphous glibenclamide in the co-amorphous blends was seen, as the formation of the thermodynamically less stable imidic acid tautomer of glibenclamide was suppressed compared to that of the pure amorphous drug. Furthermore, the co-amorphous mixtures provided a physical stability advantage over the amorphous drugs alone

The Role of Glass Transition Temperatures in Coamorphous Drug–Amino Acid Formulations

The improved physical stability associated with coamorphous drug–amino acid (AA) formulations may indicate a decrease in mobility of the amorphous drug molecules, compared to the neat amorphous form of the drug. Since the characteristic glass transition temperatures (<i>T</i>_gα and <i>T</i>_gβ) represent molecular mobility in amorphous systems, we aimed to characterize <i>T</i>_gα and <i>T</i>_gβ and to determine their role in physical stability as well as their potential usefulness to determine the presence of an excess component (either drug or AA) in coamorphous systems. Indomethacin (IND)–tryptophan (TRP) and carvedilol (CAR)–TRP were used as model coamorphous systems. The analytical techniques used were X-ray powder diffractometry (XRPD) to determine the solid-state form, dynamic mechanical analysis (DMA) to probe <i>T</i>_gα and <i>T</i>_gβ, and differential scanning calorimetry (DSC) to probe thermal behavior of the coamorphous systems. <i>T</i>_gα analysis showed a gradual monotonous increase in <i>T</i>_gα values with increasing AA concentration, and this increase in the <i>T</i>_gα value is not the cause of the improved physical stability. The <i>T</i>_gβ analysis for the IND–TRP sample with 10% drug had a <i>T</i>_gβ of 226.8 K, and samples with 20–90% drug had similar <i>T</i>_gβ values around 212.5 K. For CAR–TRP, samples with 10–40% drug had similar <i>T</i>_gβ values around 230.5 K, and samples with 50–90% drug had similar <i>T</i>_gβ values around 223.3 K. The similar <i>T</i>_gβ values in coamorphous systems at different drug ratios indicate that they in fact are the <i>T</i>_gβ of the component that is in excess to an ideal drug–AA coamorphous mixture. DSC and XRPD analysis showed that for IND–TRP, IND is in excess if the drug concentration is 30% or above and will eventually recrystallize. For CAR–TRP, CAR is in excess and recrystallizes when the drug concentration is 50% or above. We have proposed a means of estimating, on the basis of <i>T</i>_gβ, which drug to AA ratios will lead to optimally physically stable coamorphous systems that can be considered for further development

Large-Scale Biophysical Evaluation of Protein PEGylation Effects: In Vitro Properties of 61 Protein Entities

PEGylation is the most widely used method to chemically modify protein biopharmaceuticals, but surprisingly limited public data is available on the biophysical effects of protein PEGylation. Here we report the first large-scale study, with site-specific mono-PEGylation of 15 different proteins and characterization of 61 entities in total using a common set of analytical methods. Predictions of molecular size were typically accurate in comparison with actual size determined by size-exclusion chromatography (SEC) or dynamic light scattering (DLS). In contrast, there was no universal trend regarding the effect of PEGylation on the thermal stability of a protein based on data generated by circular dichroism (CD), differential scanning calorimetry (DSC), or differential scanning fluorimetry (DSF). In addition, DSF was validated as a fast and inexpensive screening method for thermal unfolding studies of PEGylated proteins. Multivariate data analysis revealed clear trends in biophysical properties upon PEGylation for a subset of proteins, although no universal trends were found. Taken together, these findings are important in the consideration of biophysical methods and evaluation of second-generation biopharmaceutical drug candidates