(M1330-09-60) Compendial Strategy to Define Composition and Quality of Polysorbates

Purpose: Polysorbates (PS) are widely used excipients, especially their recently increased use in injectables of therapeutic biological products. To address stakeholder requests to update and establish appropriate specifications for different PS used in pharmaceutical development and manufacturing, the USP Excipients Expert Committee has published two Stimuli articles in PF 47(1) [Jan. – Feb. 2021] and PF 49(4) [Jul. – Aug. 2023], respectively. (Ref. 1-2) This poster presents current compendial understanding of PS compositions, their applications, challenges, and opportunities faced in strengthening the PS compendial standards, especially the compendial effort to develop direct analytical procedures for intact PS and the proposed compendial approaches. Summary results of a survey are also presented in this poster.

Methods: The gas chromatography based Fatty Acids Composition test in both Identification and Assay sections of the current PS monograph provides important information about the starting materials used and the general distribution of fatty acids in the product. However, it lacks other important quality information that could be found using a direct analytical procedure on the intact PS to better characterize the PS composition. As part of USP’s strategy to develop a direct analytical procedure for intact PS, our initial research and method development (R&D) phase includes the following: Use of high-performance liquid chromatography (HPLC) with either a charged aerosol detector (CAD) or an evaporative light scattering detector (ELSD). Comparative studies between the HPLC-CAD and HPLC-ELSD detection methods are performed on each PS; Mass spectrometry (MS) analysis in tandem with HPLC-ELSD (or CAD) to identify various components present in the PS, including free-head groups (such as PEG sorbitan, PEG isosorbide, etc.), and various PEG sorbitan ether fatty esters (mono-, di-, and triester species), and PEG isosorbide ether fatty esters; Identifying appropriate reference standards for quantitative analysis because HPLC-CAD and HPLC-ELSD are nonlinear detection methods; Testing different PS samples from different suppliers to ensure appropriate specifications for different PS; Conducting a survey to gather feedback and engage stakeholders.

Results: The preliminary R&D results showed that the initially developed HPLC-ELSD method was suitable for the direct analysis of PS 20, but the method could not elute the higher-order esters in PS 80, PS 65 or PS 60, as shown in Figure 1. Therefore, separate methods for each of the PS should be developed, as the differences between different PS are too great. Comparative studies using ELSD and CAD detectors showed that the HPLC-ELSD had better results over CAD for PS 20, in terms of peak shapes, noise and base line etc. However, CAD shows significant benefits compared to ELSD for polysorbate 80. Due to the nonlinear nature of ELSD and CAD detectors, reference standards are needed for calibration purposes for individual PS. USP is currently in the process of identifying suitable reference standards for PS 20 direct composition analysis. Other PS will follow. The R&D preliminary results also indicated that specifications need to be flexible to support broad pharmaceutical applications. For example, groups of components (free-head groups vs esters), will be considered for each individual compendial PS. Additionally, specifications on the relative percentage of mono vs. high-order esters will be considered. A forced degradation study was also performed for PS 80 to develop a stability-indicating test method. See Figure 2. Survey results are summarized regarding the PS functionality, application, gaps, and challenges. For example, the concentration level of polysorbates in final dosage form was noted to relate to routes of administration, in terms of oral, parenteral, topical, ophthalmic, and inhalation uses. As for the functionality (multiple choices), PS used as surfactants and emulsifying agents (52%) were the most frequently rated by the respondents, followed by stabilizer (33%), crystallization inhibition (19%), lubricant (14%), gelling agent (14%), suspending/viscosity-modifying agent (9.5%), and others (5%). Detailed survey results will be presented on the poster.

Conclusion: USP has published two Stimuli articles in PF 47(1) [Jan. – Feb. 2021] and 49(4) [Jul. Aug. 2023], respectively, to engage stakeholders and obtain their input. Since it is not feasible to have a universal method for all PS, USP has been engaging stakeholders to develop suitable direct analytical methods for each individual PS. Based on the R&D study, a direct analytical procedure for PS 20 will be validated and published in PF along with suitable reference standards to facilitate the direct analysis of PS. Several PS monographs, including PS 80, PS 65 and the recently added PS 20, are under the workplan of Pharmacopeial Discussion Group for harmonization among European Pharmacopeia, Japanese Pharmacopeia and USP. USP is engaging its PDG partners in the harmonization of these PS monographs, which will provide an opportunity for broader global collaboration on setting appropriate quality control standards for PS.

References: 1) Moore D, Cawthorne R, Houck K, Sun H, Tu J, Rumbelow S, Scherer D, Rao A, Zong Y, Delaney S, Sheehan C, Liu T, Wang H. Understanding the composition and quality of polysorbates to strengthen USP-NF compendial standards. In: Pharm Forum. 47(1) [Jan – Feb] 2021.
2) Frigo T, Cawthorne R, Demeule B, Wang T, Tu J, Sun H, Kestur U, Rao A, Zong Y, Wang E, Chavan DV, Gilbert K, Sheehan C, Liu T, Wang H. USP Responses to Comments on Stimuli Article “Understanding the Composition and Quality of Polysorbates to Strengthen USP–NF Compendial Standards”. To be published in Pharm Forum. 49(4) [Jul – Aug] 2023.

Acknowledgements: This poster was based on the work of the USP Polysorbates Joint subcommittee under the Complex Excipients Expert Committee. The views expressed in this poster are those of the authors and do not reflect official views and policies of the USP, USP Council of Experts, or the authors' institutions.

Figure 1. Overlay of different PS chromatograms using an initially developed HPLC-ELSD method

Figure 2. PS 80 Forced Degradation Study (humidity and heat)
– Overlay of chromatograms at different stress time intervals using a HPLC-CAD method