Unveiling polymerization-dependent pharmacokinetics and dual oxidative metabolism of PEG600 oligomers in rats via UHPLC-MS/MS

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 (ADME) of discrete PEG600 oligomers (n = 9–18) in rats using a validated UHPLC-MS/MS method. Systemic exposure, assessed by dose-normalized AUC, was highest for shorter oligomers (n = 9–10) and declined for longer chains (n ≥ 17), while all oligomers exhibited similarly short terminal half-lives (12.7–15.2 min), indicating rapid elimination irrespective of chain length. Tissue distribution revealed pronounced renal accumulation, peaking at mid-chain lengths (n = 11–13), consistent with size-dependent glomerular filtration and tubular reabsorption. Oxidative metabolism yielded both mono- and di-carboxylated 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 ADME profile of PEG600 oligomers, highlighting the critical role of polymerization degree in governing their pharmacokinetics and informing the rational design of PEGylated drug formulations.