Dose rounding of trastuzumab deruxtecan in chinese patients: cost savings and safety outcomes in real-world study.

Trastuzumab deruxtecan is a life-saving but costly therapy for HER2-positive cancers. While dose rounding strategies have been proposed to reduce drug waste, their safety and cost-saving potential in real-world Chinese patients remain understudied. This study aimed to evaluate the cost savings of dose rounding for trastuzumab deruxtecan in China and compare the safety profiles of upward rounding, downward rounding, and no rounding groups. We conducted a retrospective real-world study of patients receiving trastuzumab deruxtecan between 2024 and 2025. Drug waste, cost savings, and dose deviations were calculated for each administration. Adverse events including nausea, vomiting, fatigue, and hematologic toxicities were compared across the three groups. Among 141 patients with 829 administrations, dose rounding down led to a cost saving of CNY 897, 840, while dose rounding up avoided 4, 368.3 mg of drug waste. Dose deviations ranged from 0.10% to 9.97%, well within the 10% acceptable limit. The incidence and severity of adverse events were comparable across groups, with no statistically significant differences observed. These findings indicate that dose rounding of trastuzumab deruxtecan to the nearest full vial, within a 10% deviation range, can significantly reduce drug waste and pharmacy costs without compromising safety. This strategy is both safe and feasible in Chinese patients and provides preliminary evidence for cautious implementation, pending validation in larger studies.