The purpose of the presented study is to understand the physicochemical properties of proteins in aqueous solutions in order to identify solution conditions with reduced attractive protein‐protein interactions, to avoid the formation of protein aggregates and to increase protein solubility. This is assessed by measuring the osmotic second virial coefficient (B22), a parameter of solution non‐ideality, which is obtained using self‐interaction chromatography. The model protein is lysozyme. The influence of various solution conditions on B22 was investigated: protonation degree, ionic strength, pharmaceutical relevant excipients and combinations thereof. Under acidic solution conditions B22 is positive, favoring protein repulsion. A similar trend is observed for the variation of the NaCl concentration, showing that with increasing the ionic strength protein attraction is more likely. B22 decreases and becomes negative. Thus, solution conditions are obtained favoring attractive protein‐protein interactions. The B22 parameter also reflects, in general, the influence of the salts of the Hofmeister series with regard to their salting‐in/salting‐out effect. It is also shown that B22 correlates with protein solubility as well as physical protein stability.

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Biological drugs intended for multi-dose application require the presence of antimicrobial preservatives to avoid microbial growth. As the presence of certain preservatives has been reported to increase protein and peptide particle formation, it is essential to choose a preservative compatible with the active pharmaceutical ingredient in addition to its preservation function. Thus, this review describes the current status of the use of antimicrobial preservatives in biologic formulations considering (i) appropriate preservatives for protein and peptide formulations, (ii) their physico-chemical properties, (iii) their in-/compatibilities with other excipients or packaging material, and (iv) their interactions with the biological compound. Further, (v) we present an overview of licensed protein and peptide formulations.

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