Impact of Time and Temperature on Glycation, Oxidation, and Functional Stability of Trastuzumab Deruxtecan (ENHERTU®) in Dextrose Infusion Bags

Trastuzumab deruxtecan (T-DXd) is a HER2-targeted antibody–drug conjugate (ADC) with a high drug-to-antibody ratio and a structurally complex design, requiring rigorous stability assessment during preparation and administration. Although the stability of the reconstituted product has been established, data on diluted T-DXd under clinically relevant storage conditions remain limited, with the Summary of Product Characteristics (SmPC) recommending use within 24 h at 2-8°C or 4 h at ≤ 30°C. This restriction may increase drug wastage, treatment costs, and the environmental burden associated with disposal of unused cytotoxic preparations. We investigated the physicochemical and functional stability of T-DXd diluted in 5% dextrose and stored in polypropylene infusion bags at 1 and 4 mg/mL. An orthogonal stability-indicating analytical platform was developed and qualified, combining size-exclusion, hydrophobic interaction, and cation-exchange chromatography, FcγRIIIa affinity chromatography, dynamic light scattering, glycan profiling, HER2-binding ELISA, and LC–MS. Forced degradation studies established method selectivity and elucidated degradation mechanisms. Ultraviolet stress induced peptide backbone cleavage, fragmentation, and marked loss of FcγRIIIa and HER2-binding activities, whereas thermal and light stress promoted aggregation, charge heterogeneity, oxidation, and non-enzymatic glycation, resulting in acidic variants and reduced binding potency. No payload loss or deconjugation was detected, confirming the stability of the GGFG–DXd linker–payload system. Under real-use conditions, diluted T-DXd remained physicochemically and functionally stable for up to 28 days at 2–8°C, while storage at 25°C accelerated oxidative and glycation-mediated degradation. These findings support extended refrigerated storage of diluted T-DXd and provide mechanistic insights into ADC degradation pathways relevant to pharmaceutical development and hospital pharmacy practice.