Study of surfactant-preservative and protein-preservative interactions in multi-dose injectable formulation

Abstract: Multidose injectable formulations require a preservative such as phenol to ensure sterility and protection against microbial contamination during clinical use. However, it is known that the interaction between these components and non-ionic surfactants such as polysorbate 80, also found in this type of formulations, present incompatibilities, which can lead to decreases in the efficacy of the product. This incompatibility is linked to a decrease in the cloud point of the surfactant. The presence of other common components in this type of formulations, such as salt, proteins or non-ionic tonicity adjusting agents are also known to influence this phenomenon. Furthermore, it’s known that preservatives can lead to increased aggregation in protein-based formulations as a consequence of preservative-protein interaction. In order to study these incompatibilities, different concentration titrations were carried out in which the emergence of the cloud point was monitored by simultaneous measurement of light scattering. In general, these titrations consisted of the addition of phenol to samples containing polysorbate 80, salt, protein and tonicity adjusting agents in varying concentrations. Additionally, preservative-protein interaction was studied by complementary concentration titrations and sample-specific analysis by small-angle X-ray scattering. Results obtained in the study indicate that the presence of phenol, at concentrations within the range commonly used in multi-dose injectable formulations, leads to a reduction in the cloud point of polysorbate 80 down to 25ºC. In addition, the presence of other components such as salt, somatropin or mannitol is shown to decrease the phenol concentration required for the appearance of this phenomenon. Moreover, results suggest that the interaction between somatropin and phenol leads to protein aggregation, which is significantly enhanced by the presence of salt.