OBJECTIVES: The first FDA-approved biosimilar was launched in 2015: Filgrastim-sndz (Zarxio), a biosimilar for the reference drug filgrastim (Neupogen). Filgrastim is a granulocyte colony-stimulating factor used to prevent and treat neutropenia. In this study, we examined the association between site of care and drug cost across reference filgrastim, tbo-filgrastim (Granix; a version of filgrastim approved as a biosimilar in Europe and as a new drug in the United States), and biosimilar filgrastim administrations among the commercially insured. STUDY DESIGN: Retrospective study using administrative claims data. METHODS: We used OptumLabs Data Warehouse to identify the site of care of each short-acting filgrastim administration among commercial enrollees between January 1, 2014, and December 31, 2019. RESULTS: For each filgrastim product, model-adjusted median drug costs were higher in the outpatient hospital setting than for the same drug administered in the office setting. Comparing drug costs within the same setting, in the office setting, costs of biosimilar and tbo-filgrastim were $103.61 and $94.07 lower than reference filgrastim, respectively (P < .001 for each comparison). In the outpatient hospital setting, adjusted median costs for tbo-filgrastim were lower than those for reference filgrastim (-$132.90; P < .001), but adjusted median costs of the biosimilar were slightly higher ($20.50; P = .025). CONCLUSIONS: Although previous work has found lower costs for biosimilar filgrastim compared with reference filgrastim, here we found that site of care can change this calculus, reducing savings. After adjusting for patient characteristics and geography, we found that drug cost savings for biosimilar filgrastim were limited to the office setting, with no savings in the outpatient hospital setting.
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