Analytical method development, validation, and out-of-specification investigations for polyethylene glycol

Abstract

This work was motivated by the United States Pharmacopeia monograph modernization initiative and European directorate for the quality of medicines and healthcare. An out-of-specification (OOS) occurrence prompted OOS investigations for the cGMP (cGMP refers to the Current Good Manufacturing Practice regulations enforced by the FDA) release testing of residual ethylene oxide in polyethylene glycol (PEG) according to the standards detailed within the United States Pharmacopeia/National Formulary (USP-NF) for polyethylene glycol, and the European Pharmacopoeia (Ph. Eur.) for macrogols. During the OOS root cause investigations, we observed a PEG degradant and identified it as methyl formate, which co-elutes with ethylene oxide using the GC (gas chromatography) methods published in current USP-NF and Ph. Eur. for PEGs. To address this, a novel method utilizing static headspace gas chromatography with flame ionization detection (HS-GC-FID) was developed to test various grades of PEGs for the presence of residual ethylene oxide, along with other process related impurities and degradation products. With this new method, ethylene oxide, a known genotoxic impurity and IARC (International Agency for Research on Cancer) Class 1 human carcinogen, can be well resolved from methyl formate, a newly identified and comparatively innocuous degradant derived from PEG. The currently available official compendial methods are unable to separate the specific impurities in PEGs. However, the new GC method presented in this paper has been shown to have a high and unique selectivity, allowing for baseline separations (chromatographic resolutions greater than 1.5) of all related impurities in PEGs, which is a challenging task. Additionally, this method has been found to be stability-indicating based on a forced degradation study. During stress stability study of PEGs involving acid, alkali, heat, light, and oxidation, some other PEG degradants, including formaldehyde, were identified. It is possible that formaldehyde undergoes a disproportionation reaction known as the Cannizzaro reaction, leading to the formation of formic acid and methanol. The formic acid then undergoes an esterification reaction with methanol to produce methyl formate. To the best of our knowledge, this is the first stability-indicating HS-GC-FID method that accomplishes this separation in a single run, and it was successfully validated as per ICH (the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use) guidelines. Therefore, this method is suitable for the conduct of cGMP batch release and stability testing of PEGs in regulated quality control (QC) laboratories.