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Provider Differences in Biosimilar Uptake in the Filgrastim Market

Alice J. Chen, PhD; Rocio Ribero, PhD; and Karen Van Nuys, PhD
The speed and extent of biosimilar penetration differ across provider types. Provider awareness and incentives are significantly associated with biosimilar uptake.

To identify differences in biosimilar uptake across providers and to examine the association between provider biosimilar uptake and observable practice-level characteristics.

Study Design: A retrospective analysis of 100% of a commercial medical claims database from June 2015 to June 2018.

Methods: We focused on providers of biologic (Neupogen) and biosimilar (Zarxio) filgrastim. We compared trends in biosimilar uptake across 2 dimensions: provider’s place of service and provider’s prescribing exclusivity. We then used multivariate regression analysis to estimate the association between any biosimilar uptake and practice-level characteristics, controlling for geography and time fixed effects.

Results: Relative to hospital-based providers, office-based providers were earlier and quicker adopters of the biosimilar filgrastim. Across all places of service, providers predominantly prescribed either the biosimilar or biologic, exclusively, for all their patients. Any biosimilar uptake was more common among providers in office-based settings, providers with larger practice sizes, and providers with a higher share of health maintenance organization patients, nonwhite patients, and younger patients.

Conclusions: This study uncovers important associations between provider practice characteristics and biosimilar uptake. Our findings suggest that provider awareness and incentives can be important levers to strengthen US biosimilar market penetration and competition.

Am J Manag Care. 2020;26(5):208-213.
Takeaway Points
  • After 3 years, the share of filgrastim claims that are biosimilar rose to 60% among office-based providers and 49% among providers at outpatient hospitals.
  • Very few providers simultaneously offered both biologic and biosimilar filgrastim; providers generally prescribed only 1 version.
  • Office-based settings and health maintenance organization contracting are associated with increased biosimilar uptake and should be further examined.
Accounting for 38% of all prescription drug spending in 2015 and 70% of drug spending growth from 2010 to 2015, biologic drugs are fueling interest in policies to develop and use biosimilars.1 Biosimilars are clinically equivalent therapeutic alternatives to biologics, and some policy makers have conjectured that biosimilars can reduce drug spending, as generics have done for small molecules.2-4 Although biosimilars are widely prescribed in Europe, they are less common in the United States, in part because of regulatory and developmental differences. As of May 2019, the FDA had approved 19 biosimilars, whereas the European Medicines Agency had approved 61.5 Of the 19 US-approved biosimilars, only 7 had been launched by May 2019.

The penetration of approved biosimilars has also disappointed some observers. Many approved biosimilars in the United States experience delayed launches because of patent litigation. For example, 3 approved biosimilars to trastuzumab (Herceptin), a therapy for early-stage breast cancer, faced patent infringement litigation before coming to market. Early surveys suggest that uptake has been hampered by factors such as insufficient provider awareness and lackluster price competition.6,7 Although biosimilars appear to generate some reductions in net prices, prices may not decline as quickly or significantly as some expect.8 Recently, some investigators have even suggested that biosimilars should be abandoned altogether in favor of government-imposed price controls on originator biologics once their patent protection has lapsed.9,10

Assessing the viability of the US biosimilar market requires a better understanding of factors that have affected biosimilar adoption. Once a biosimilar has regulatory approval, providers play a key role in the decision to prescribe it or its reference biologic.11 In many cases, biologics and their biosimilars are physician administered, and physicians have discretion over which drug to prescribe. Even when a biologic is filled at a retail pharmacy, pharmacists cannot automatically substitute an approved biosimilar for a biologic prescription, as they can do for generic versions of small molecule drugs, because the FDA has not yet established that any biosimilars and biologics on the market are interchangeable; pharmacists must dispense only the drug prescribed by the provider.12 In July 2018, then–FDA Commissioner Scott Gottlieb, MD, concluded that “the ability for [biosimilars] to penetrate clinical practice, and gain acceptance, is still not firm,” and the FDA’s Biosimilar Action Plan consequently prioritized resources to improve provider understanding of biosimilar drugs.13,14

In this study, we explore the dynamics of biosimilar uptake. Our study represents the first provider-specific analysis of the US market uptake of a biosimilar drug relative to its biologic.

Although our analysis cannot uncover causal relationships between provider characteristics and biosimilar uptake, it identifies factors that are associated with biosimilar use. Uncovering any such relationship is a necessary first step in highlighting whether provider incentives can be used to increase biosimilar adoption.


Study Sample

We focus on the uptake of the first US-approved biosimilar drug, Zarxio (filgrastim-sndz), the only biosimilar in the United States with more than 2 years of data by 2018. Zarxio is a biosimilar to Neupogen (filgrastim), a man-made granulocyte colony-stimulating factor (G-CSF) used to treat conditions such as febrile neutropenia. G-CSF drugs are predominantly administered by physicians in an outpatient setting to patients with cancer who are also receiving chemotherapy or undergoing bone marrow transplants or to patients with severe chronic neutropenia.15

First approved in the United States in 1991, Neupogen’s US patent expired in December 2013. Granix (tbo-filgrastim), which is not considered a biosimilar to Neupogen in the United States, entered the US market in November 2013. Although Granix’s structure, formulation, and mechanism do not differ significantly from Neupogen’s, Granix was reviewed prior to the adoption of the Biologics Price Competition and Innovation Act of 2009.16 As such, it was approved through the biologics license pathway, and it was approved for only 1 of the 5 filgrastim indications.17 Therefore, Granix covers a different on-label market than Neupogen. In contrast, Zarxio—approved in March 2015 and launched in September 2015—was the first drug approved through the biosimilar pathway, and it was approved for all 5 of the filgrastim indications. Because our focus is on the US biosimilar market, our analysis focuses on Neupogen (the biologic) and Zarxio (its biosimilar). However, in the eAppendix (available at, we show that including Granix in our sample does not materially change the results of our analysis.

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