Stabilization of a polypeptide in non-aqueous solvents

Strategies to Stabilize Dalbavancin in Aqueous Solutions; Section-1: the Effects of Metal Ions and Buffers

PURPOSE

The effect of monovalent (Na+ and K+) and divalent (Ca2+, Mg2+, and Zn2+) metal ions combined with citrate or acetate buffers (pH 4.5) on the stability of dalbavancin in aqueous solutions was investigated.

METHOD

RP-HPLC and HP-SEC were used to evaluate the stability of aqueous solutions of dalbavancin in different combinations of buffers and metal ions after four weeks of storage at 5°C and 55°C. A long-term study of formulations with divalent metal ions was conducted over six months at 5°C., 25°C and 40°C using RP-HPLC.

RESULTS

All formulations in citrate buffered solutions precipitated. Dalbavancin solutions in 10 mM acetate buffer at 55°C were more stable in 10 mM CaCl2, 5 mM ZnCl2 and 10 mM MgCl2 than those containing 2 mM NaCl or 5 mM KCl, although the MgCl2 formulations precipitated slightly. No significant effect was observed for any of the divalent metal ions at 40°C for six months.

CONCLUSION

Dalbavancin's stability in solution was improved by a combination of acetate and divalent metal ions at 55°C for four weeks. No effect was observed with acetate or metal ions alone, and no effect was observed after six months at 40°C suggesting that acetate and divalent metal ions together interact with dalbavancin via a thermally activated step to inhibit hydrolysis of the drug.

Strategies To Stabilize Dalbavancin in Aqueous Solutions; Section 3: The Effects of 2 Hydroxypropyl-β-Cyclodextrin and Phosphate Buffer with and without Divalent Metal Ions

PURPOSE

New formulations of the glycopeptide drug dalbavancin containing 2-hydroxpropyl-β-cyclodextrin (2HPβCD) with or without divalent metal ions in phosphate buffer (pH 7.0) were tested to evaluate whether these excipients influence the aqueous solution stability of dalbavancin.

METHOD

Recovery of dalbavancin from phosphate buffered solutions at pH 7.0 with different concentrations of 2HPβCD and a divalent metal ion (Ca2+, Mg2+, or Zn2+) was evaluated by RP-HPLC and HP-SEC after four weeks of storage at 5°C and 55°C. A long-term study of formulations with 2HPβCD and Mg2+ was carried out over six months at 5°C, 25°C, and 40°C using RP-HPLC.

RESULTS

Dalbavancin solutions with either 5.5 mM or 55 mM 2HPβCD were significantly more stable with Mg2+ than with the other divalent metal ions, both at 55°C for four weeks and at 40°C for six months. Dalbavancin was found to be more stable in aqueous solutions at a concentration of 1 mg/mL than at 20 mg/mL with 2HPβCD and Mg2+ at 40°C for six months.

CONCLUSION

The results suggest that 2HPβCD forms an inclusion complex with dalbavancin that slows the formation of the major degradant, mannosyl aglycone (MAG). The effect of 2HPβCD is increased in the presence of Mg2+ and phosphate at pH 7.0, and the complex is more stable at a dalbavancin concentration of 1 mg/mL than at 20 mg/mL. These observations point towards the possibility of formulating a dalbavancin injection solution with a long shelf life at room temperature and physiological pH.

Designing Formulation Strategies for Enhanced Stability of Therapeutic Peptides in Aqueous Solutions: A Review

Over the past few decades, there has been a tremendous increase in the utilization of therapeutic peptides. Therapeutic peptides are usually administered via the parenteral route, requiring an aqueous formulation. Unfortunately, peptides are often unstable in aqueous solutions, affecting stability and bioactivity. Although a stable and dry formulation for reconstitution might be designed, from a pharmaco-economic and practical convenience point of view, a peptide formulation in an aqueous liquid form is preferred. Designing formulation strategies that optimize peptide stability may improve bioavailability and increase therapeutic efficacy. This literature review provides an overview of various degradation pathways and formulation strategies to stabilize therapeutic peptides in aqueous solutions. First, we introduce the major peptide stability issues in liquid formulations and the degradation mechanisms. Then, we present a variety of known strategies to inhibit or slow down peptide degradation. Overall, the most practical approaches to peptide stabilization are pH optimization and selecting the appropriate type of buffer. Other practical strategies to reduce peptide degradation rates in solution are the application of co-solvency, air exclusion, viscosity enhancement, PEGylation, and using polyol excipients.

Glycopeptide antibiotic drug stability in aqueous solution

Glycopeptide antimicrobials are a class of naturally occurring or semi-synthetic glycosylated products that have shown antibacterial activity against gram-positive organisms by inhibiting cell-wall synthesis. In most cases, these drugs are prepared in dry powder (lyophilized) form due to chemical and physical instability in aqueous solution; however, from an economic and practical point of view, liquid formulations are preferred. Researchers have recently found ways to formulate some glycopeptide antibiotic therapeutic drugs in aqueous solution at refrigerated or room temperature. Chemical degradation can be significantly slowed by formulating them at a defined pH with specific buffers, avoiding oxygen reactive species, and minimizing solvent exposure. Sugars, amino acids, polyols, and surfactants can reduce physical degradation by restricting glycopeptide mobility and reducing solvent interaction. This review focuses on recent studies on glycopeptide antibiotic drug stability in aqueous solution. It is organized into three sections: (i) glycopeptide antibiotic instability due to chemical and physical degradation, (ii) strategies to improve glycopeptide antibiotic stability in aqueous solution, and (iii) a survey of glycopeptide antibiotic drugs currently available in the market and their stability based on published literature and patents. Antimicrobial resistance deaths are expected to increase by 2050, making heat-stable glycopeptides in aqueous solution an important treatment option for multidrug-resistant and extensively drug-resistant pathogens. In conclusion, it should be possible to formulate heat stable glycopeptide drugs in aqueous solution by understanding the degradation mechanisms of this class of therapeutic drugs in greater detail, making them easily accessible to developing countries with a lack of cold chains.

A new strategy to stabilize oxytocin in aqueous solutions: I. The effects of divalent metal ions and citrate buffer

In the current study, the effect of metal ions in combination with buffers (citrate, acetate, pH 4.5) on the stability of aqueous solutions of oxytocin was investigated. Both monovalent metal ions (Na(+) and K(+)) and divalent metal ions (Ca(2+), Mg(2+), and Zn(2+)) were tested all as chloride salts. The effect of combinations of buffers and metal ions on the stability of aqueous oxytocin solutions was determined by RP-HPLC and HP-SEC after 4 weeks of storage at either 4°C or 55°C. Addition of sodium or potassium ions to acetate- or citrate-buffered solutions did not increase stability, nor did the addition of divalent metal ions to acetate buffer. However, the stability of aqueous oxytocin in aqueous formulations was improved in the presence of 5 and 10 mM citrate buffer in combination with at least 2 mM CaCl(2), MgCl(2), or ZnCl(2) and depended on the divalent metal ion concentration. Isothermal titration calorimetric measurements were predictive for the stabilization effects observed during the stability study. Formulations in citrate buffer that had an improved stability displayed a strong interaction between oxytocin and Ca(2+), Mg(2+), or Zn(2+), while formulations in acetate buffer did not. In conclusion, our study shows that divalent metal ions in combination with citrate buffer strongly improved the stability of oxytocin in aqueous solutions.

Stability of protein pharmaceuticals: an update

In 1989, Manning, Patel, and Borchardt wrote a review of protein stability (Manning et al., Pharm. Res. 6:903-918, 1989), which has been widely referenced ever since. At the time, recombinant protein therapy was still in its infancy. This review summarizes the advances that have been made since then regarding protein stabilization and formulation. In addition to a discussion of the current understanding of chemical and physical instability, sections are included on stabilization in aqueous solution and the dried state, the use of chemical modification and mutagenesis to improve stability, and the interrelationship between chemical and physical instability.