[The Impact of Biosimilar Adoption on Drug Utilization and Cost in Chemotherapy-A Single Center Retrospective Study].

Yokohama City University Hospital recommends the use of biosimilars (BS) in newly diagnosed patients. Previous studies have focused on cost reductions through BS introduction, which compared only identical components. In contrast, this study assesses changes in the usage of drugs within the same therapeutic class. We analyzed the number of vials of anti‒CD20 antibodies used from 2017 to 2021 and anti‒VEGF antibodies used from 2018 to 2022, before and after the introduction of rituximab and bevacizumab BS, respectively. Volume shares and drug costs for each formulation were calculated annually. The drug cost reduction ratio was determined by comparing actual drug costs with hypothetical costs if only brand‒name drugs were used. The average drug cost per prescription was also calculated. From 2017 to 2021, the share of brand rituximab was decreased from 100.0% to 0.0%, while rituximab BS was increased from 0.0% to 93.9%, and obinutuzumab was increased from 0.0% to 6.1%. Although BS reduced drug costs by 22.9% in 2021, the average cost per prescription increased by 30.0%. From 2018 to 2022, the share of brand bevacizumab was decreased from 89.5% to 3.0%, while bevacizumab BS was increased from 0.0% to 96.5%, with ramucirumab and aflibercept beta showing decreased usage. BS reduced drug costs by 64.7%, and the average cost per prescription dropped by 65.5%. The introduction of BS significantly reduced drug costs, though changes in prescription practices affected overall costs. Future assessments should consider clinical guidelines and evaluate drugs across therapeutic classes to provide a more comprehensive view of BS impact.