Abstract
IMPORTANCE: Biosimilar competition has been associated with in lower prices and decreased US health care spending, but this has not consistently led to lower out-of-pocket (OOP) costs for commercially insured patients using these medications. OBJECTIVE: To investigate whether biosimilar competition was associated with lower OOP spending for Medicare patients who used biologics. DESIGN, SETTING, AND PARTICIPANTS: This cross-sectional study used an event study design. Participants were patients with Medicare Advantage coverage in a national commercial claims database (Optum's deidentified Clinformatics Data Mart Database) who used 1 of 7 clinician-administered biologics (filgrastim, infliximab, pegfilgrastim, epoetin alfa, bevacizumab, rituximab, and trastuzumab) from 2009 to 2022. Data were analyzed from April to November 2025. EXPOSURE: The calendar year when the first biosimilars entered the market for each drug. MAIN OUTCOMES AND MEASURES: The primary outcome was annual OOP spending for all doses of the biologic that a patient received in each year. Two-part regression models were used to estimate mean annual OOP spending in each year, adjusted for patient age, sex, US Census region, diagnosis, and place of service. Results were stratified by whether patients paid coinsurance or deductibles vs those who only paid copayments. RESULTS: A total of 273 774 patient-years for the 7 drugs were analyzed. Patients had a mean (SD) age of 76 (8) years, 57.6% were female, 53.4% used biologics to treat cancer, 49.7% received biologics in outpatient clinics, and 13.0% received biosimilars. Overall, 52.2% of patients paid coinsurance or deductibles, 5.2% paid only copayments, and 40.8% paid no OOP costs. Across the drugs in the cohort, mean annual OOP costs decreased by $94 (95% CI, -$105 to -$84) after competition, from $233 (95% CI, $228 to $237) in the year before biosimilar competition to $165 (95% CI, $158 to $172) 4 years after competition. Annual OOP costs decreased for all 7 drugs, and decreases were larger among patients who paid coinsurance or deductibles, compared with those who only paid copayments. CONCLUSIONS AND RELEVANCE: This cross-sectional study found that biosimilar competition was associated with lower OOP spending for Medicare patients, likely because many patients paid a percentage of drug costs. These findings suggest that by reducing OOP spending, biosimilar competition can improve access and adherence to biologic medications for Medicare patients.