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Researchers Find Varied Uptake of Biosimilars in Medicare Part D


While filgrastim biosimilars had substantial uptake, there was low uptake of infliximab biosimilars. In addition, there was a lack of price competition.

Use of filgrastim and infliximab products increased among Medicare beneficiaries from 2016 to 2019, but while there was lower total annual spending for filgrastim products, the total spending for infliximab increased, according to a study published in JAMA Network Open.

The majority of biosimilar claims are covered under Medicare Part B due to the administration in physician practices and outpatient departments, with a portion also covered under Medicare Part D.

“With ongoing deliberations on drug pricing legislation that would enable government price negotiation, we sought to understand whether biosimilars are associated with reduced spending in Part D, where insurers and pharmacy benefit managers are able to negotiate drug prices,” the authors explained.

They evaluated utilization trends for filgrastim and infliximab products using the 2015 to 2019 Medicare Part D Drug Spending Dashboard. These 2 products had the first FDA-approved biosimilars since the Biologics Price Competition and Innovation Act of 2009 created an approval pathway for biological products that are biosimilar or interchangeable with an FDA-approved originator biologic.

The filgrastim products covered were the originator product, Neupogen, and the biosimilars Granix (approved August 2012 and launched November 2013) and Zarxio (approved March 2015 and launched September 2015). The infliximab products evaluated were the originator product, Remicade, and the biosimilars Inflectra (approved April 2016 and launched November 2016) and Renflexis (approved May 2017 and launched July 2017).

Overall, the researchers found that there was substantial uptake of filgrastim biosimilasr in Medicare Part D, but low uptake of infliximab biosimilars during the time studied. They suggested that a lower uptake in Part D may be the result of originator products having preferred formulary placement on Part D plans.

Utilization of both infliximab and filgrastim increased for Medicare Part D during the time frame with the total filgrastim claims increasing 15% and the total infliximab claims increasing 41%. While spending per beneficiary for Neupogen decreased 5.3%, it increased 37.5% for Remicade.

The researchers found:

  • Annual spending on filgrastim biosimilars increased from 2% of total spending on filgrastim products in 2015 to 56%, surpassing the originator product, in 2019.
  • In comparison, the share of total spending on infliximab biosimilars only increased from less than 1% in 2017, the first year a biosimilar was approved, to 3.6% in 2019.
  • While total annual Part D spending on originator filgrastim decreased by 7% during the study time period, the total annual Part D spending on originator infliximab increased by 17%.

“While conventional economic wisdom would suggest that biosimilar competition would reduce prices and spending per beneficiary, the complexity of the US pharmaceutical market, with proprietary discounts and rebates, may hinder market competition,” the authors noted.

They added that policy makers should be concerned about the lack of price competition, and that redesigning Part D benefit could increase the use of biosimilars by giving them more favorable formulary placement or reducing prior authorization requirements. Finally, legislation may be needed since most of the payment for infliximab and filgrastim occur on Part B, which means insurers “may not have sufficient market power to leverage purchasing power” in Part D.

“Thus, Congressional legislation should ensure purchasers have real power when negotiating with drug manufacturers, whether through representing a high-purchasing volume or through price limits such as internal or external reference pricing,” they concluded.


Hussaini SMQ, Gupta A, Anderson KE, Ballreich JM, Hersch Nicholas L, Alexander GC. Utilization of filgrastim and infliximab biosimilar products in Medicare Part D, 2015-2019. JAMA Netw Open. 2022;5(3):e221117. doi:10.1001/jamanetworkopen.2022.1117

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