Physician, Practice, and Patient Characteristics Associated With Biosimilar Use in Medicare Recipients

IMPORTANCE: Biosimilars, or highly similar versions of complex biologic drugs, have the potential to slow drug spending growth; however, biosimilar uptake in the United States has been slow. Little is known about barriers to biosimilar uptake following drug launch. OBJECTIVE: To examine the patient, physician, and practice characteristics associated with biosimilar use in the Medicare population. DESIGN, SETTING, AND PARTICIPANTS: This cross-sectional study used regression analysis to estimate the association between biosimilar use and various characteristics. Medicare fee-for-service beneficiaries who received a filgrastim product or an infliximab product between the launch of a class’s first biosimilar (quarter 3 2015 for filgrastim-sndz and quarter 4 2016 for infliximab-dyyb) and December 2018. Data analysis was conducted from March to November 2020. EXPOSURES: Patient demographic characteristics and product clinical indications; physician demographic characteristics, specialty, and volume of filgrastim or infliximab biologic administration; hospital size, ownership, 340B status, academic medical center status, and system affiliation; physician office size and multispecialty status. MAIN OUTCOMES AND MEASURES: Administration of a filgrastim or infliximab biosimilar. RESULTS: The final filgrastim sample included 25 870 patients (11 857 [45.8%] men; 14 224 [55.0%] aged 65-74 years; 22 617 [87.4%] White individuals) who had 259 178 administrations (79 017 [30.5%] biosimilar administrations), and the final infliximab sample included 14 786 patients (4765 [32.2%] men; 8773 [59.3%] aged 65-74 years; 13 467 [91.1%] White individuals) who had 174 973 administrations (9012 [5.2%] biosimilar administrations). In adjusted analyses, no patient demographic characteristics and 2 of 9 clinical indications (22.2%) were associated with biosimilar use (filgrastim, neutropenia: adjusted difference, −2.0 [95% CI, −3.9 to −0.2] percentage points; P = .03; infliximab, Crohn disease: adjusted difference, −1.8 [95% CI, −2.9 to −0.8] percentage points; P = .001). Several physician characteristics were associated with biosimilar administrations, including high filgrastim or infliximab prescribing volume (high vs low volume, filgrastim: adjusted difference, 3.6 [95% CI, 1.5 to 5.8] percentage points; P = .001; infliximab: adjusted difference, 1.2 [95% CI, 0.3 to 2.2] percentage points; P = .007) and specialty (eg, hematologist-oncologists vs primary care, filgrastim: adjusted difference, −3.0 [95% CI, −5.4 to −0.5] percentage points; P = .02). Numerous practice characteristics were associated with biosimilar use, including practice setting (outpatient hospital department vs office practice, filgrastim: adjusted difference, −16.1 [95% CI, −18.1 to −14.1] percentage points; P < .001; infliximab: adjusted difference, 3.0 [95% CI, 2.2 to 3.7] percentage points; P < .001) and hospital outpatient department ownership status (for-profit vs not-for-profit, filgrastim: adjusted difference, −17.4 [95% CI, −21.6 to −13.3] percentage points; P < .001; infliximab: adjusted difference, 10.8 [95% CI, 6.7 to 14.9] percentage points; P < .001). CONCLUSIONS AND RELEVANCE: In this study, practice setting and hospital ownership status had the largest associations with biosimilar usage, suggesting practices play a role in steering physicians toward certain medications. However, the types of practices with high biosimilar use differed by drug class. Further research is needed to understand the reasons for these differences across drug classes.