A comparative study of the oxidative degradation of poloxamer 188, polysorbate 20 and polysorbate 80 in various buffered solutions.

The importance of biologics has increased over the last few decades. Since proteins in liquid formulations tend to form protein particles in response to external stress factors, surfactants are added to prevent this. Currently, polysorbates (PSs) 20 and 80 are mainly used for this purpose. However, alternatives are being investigated, as PSs have stability issues, primarily due to oxidative or enzymatic degradation. The most frequently discussed alternative, which is already used in commercial biologics, is poloxamer 188 (P188). However, this triblock copolymer, which consists of a polyoxypropylene block flanked by polyoxyethylene units, may also degrade through oxidative processes. Surprisingly, there are no direct comparative stability studies for PSs and P188. Therefore, the present study compared the oxidative degradation profiles of PS20 and PS80 with those of P188 in various relevant buffer systems. To this end, the formulations were subjected to stress in the form of 50 ppb (approximately 0.9 µM) of Fe2+ and light in the visible range, in line with their exposure during pharmaceutical production. Samples that received neither an iron spike nor light served as controls. The solutions contained 0.4mg·mL-1 PS20, PS80, or P188, respectively. The surfactants were formulated in either a 25 mM acetate, citrate, or histidine buffer solution (all pH 5.5) or in pure water. Significant differences were observed between these buffers, with greater effects at higher temperatures. The stability of the surfactant depended greatly on the buffer and the applied stress. All surfactants exhibited high rates of oxidative degradation when formulated in acetate buffer or pure water. PSs demonstrated the highest overall stability in citrate buffer, while P188 remained most stable in histidine, as well as in citrate buffer. However, both PSs exhibited instability in the presence of iron and light in histidine buffer, a phenomenon not observed in P188.