Unveiling polymerization-dependent pharmacokinetics and dual oxidative metabolism of polyethylene glycol 600 oligomers in rats via ultra-high-performance liquid chromatography coupled to tandem mass spectrometry.

A comprehensive understanding of the in vivo fate of low-molecular-weight polyethylene glycol (PEG) oligomers is essential for optimizing PEGylated therapeutics. This study delineates the polymerization-dependent absorption, distribution, metabolism, and excretion of discrete PEG600 oligomers (n = 9-18) in rats using a validated ultrahigh-performance liquid chromatography-tandem mass spectrometry method. Systemic exposure, assessed by dose-normalized area under the plasma concentration-time curve, was highest for shorter oligomers (n = 9-10) and declined for longer chains (n ≥ 17), whereas all oligomers exhibited similarly short terminal half-lives (12.7-15.2 minutes), indicating rapid elimination irrespective of chain length. Tissue distribution revealed pronounced renal accumulation, peaking at midchain lengths (n = 11-13), consistent with size-dependent glomerular filtration and tubular reabsorption. Oxidative metabolism yielded both monocarboxylated and dicarboxylated derivatives, confirming active enzymatic processing. Excretion studies demonstrated chain length-dependent elimination, with reduced recovery of longer oligomers, suggesting substantial in vivo biodegradation. These findings provide the first monomer-resolved absorption, distribution, metabolism, and excretion profile of PEG600 oligomers, highlighting the critical role of polymerization degree in governing their pharmacokinetics and informing the rational design of PEGylated drug formulations. SIGNIFICANCE STATEMENT: This study provides the monomer-resolved insight into the in vivo fate of polyethylene glycol 600 oligomers, revealing that chain length critically governs their pharmacokinetics, tissue distribution, and elimination. The identification of dual oxidative metabolic pathways and substantial biodegradation of longer oligomers offers guidance for the rational design and safety evaluation of PEGylated therapeutics.