Biosimilar uptake of filgrastim and impact on spending in Medicare Part D from 2015 to 2019.

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67 Background: The introduction of a filgrastim biosimilar in 2014 was associated with substantial cost savings in Medicare Part B and Medicaid programs. However, Medicare Part D is unique since it is unable to directly negotiate prices with drug manufacturers. We sought to investigate the uptake of filgrastim biosimilars and impact on spending among Part D beneficiaries. Methods: We evaluated utilization trends for filgrastim (Neupogen), filgrastim-sndz (Zarxio), and tbo-filgrastim (Granix) using the 2015-2019 Medicare Part D Prescription Drug Event data. We conducted a retrospective cross-sectional review of annual spending, number of beneficiaries, number of claims, spending per beneficiary, and spending per dosage unit. We excluded filgrastim-aafi (Nivestym) due to recent approval and adjusted for inflation using 2019 dollars. Results: In 2019, total aggregate Part D spending on filgrastim products was $78 million. From 2015 to 2019, the biosimilar share of total aggregate spending increased from $1.8 million (2%) to $44 million (56%), with combined biosimilar spending (Zarxio and Granix) eclipsing originator Neupogen in 2018 (within 4 years of FDA approval of Zarxio). Total spending on Neupogen reduced 58% from 2015 to 2019. While biosimilar uptake progressively increased every year, total aggregate spending on all filgrastim forms reduced only 7% from 2015 to 2019 ($84 million to $78 million). For all 3 forms, from 2015 to 2019, trends in spending were: average spending per claim ($3193 to $2549, -20%), average spending per beneficiary ($5880 to $6722, +15%), and average spending per dosage unit of filgrastim ($583 vs $571, -2%). Detailed results in Table. Conclusions: We demonstrate that the significant uptake of biosimilar filgrastim products in Medicare Part D from 2015 to 2019 was associated with a small decrease in aggregate spending, essentially unchanged per unit spending, and increased spending per beneficiary on filgrastim products. Our findings contrast with experiences across Medicare Part B and Medicaid, that demonstrated significant cost savings with biosimilar filgrastim uptake. This may be due to inability of Medicare Part D to directly negotiate prices with manufacturers (in contrast to Medicare Part B and Medicaid), supporting ongoing Congressional policy being debated in the United States Senate (H.R. 3).[Table: see text]