OBJECTIVES:

Biosimilars become available after the originator’s period of market exclusivity and offer the possibility of price competition. Biosimilar market uptake has so far been variable. We evaluated patient and provider factors associated with use of biosimilar filgrastim, the first biosimilar marketed in the US.

METHODS:

We identified new filgrastim users from March 6, 2015 (date first biosimilar was marketed) through March 31, 2022 (end of available data) using a national claims database of commercially insured and Medicare Advantage patients. Patients had 365 days of continuous prior enrollment, during which they had no filgrastim use and baseline characteristics were measured, including age, sex, race/ethnicity, comorbidities, health care service use, commercial vs. Medicare Advantage insurance, place of service, physician’s region, and years since market entry. We used logistic regression to identify which factors were independently associated with use of biosimilar vs. originator filgrastim.

RESULTS:

Among 30,827 new filgrastim users, the mean age was 65.5 years, 68.8% were White, 44.4% were from the Southern US, and 46.5% received filgrastim in a clinic setting. Overall, 16,606 (62.4%) used a biosimilar version; biosimilar use increased from 1% in 2015 to 95% in 2022 (adjusted OR=1.98/year, 95% CI: 1.81-2.18). Factors associated with higher biosimilar use included Hispanic race/ethnicity (adjusted OR=1.25 vs. White patients, 95% CI: 1.14-1.37), and receipt of filgrastim in a clinic setting (adjusted OR=1.69 vs. outpatient hospital, 95% CI: 1.59-1.80). Patients <18 years old were less likely to use a biosimilar (adjusted OR=0.17 vs. age >65, 95% CI: 0.12-0.23). Highest biosimilar use was in the Western and Southern US regions.

CONCLUSIONS:

We identified factors associated with variation in biosimilar uptake related to patient demographics, geography, and clinical site of care. These results can inform policy interventions to improve uptake of less expensive biosimilars, which could yield health care savings and improve affordability and access to biologic medications.