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Infliximab biosimilars have taken an increasing share of prescriptions for the first tumor necrosis factor (TNF) inhibitor to win approval, but some payers have been more willing than others to cover these products -- with the U.S. government so far being the least willing.

From 2016 to 2022, private insurance, Medicaid, and Medicare all substantially increased the proportion of infliximab prescriptions for which biosimilar versions were provided. But the increase was much slower under Medicare compared with the other two payer types, according to Eric T. Roberts, PhD, of the University of California San Francisco, and colleagues .

Specifically, mean annual rate increases during 2016-2020 -- the period in which the first two biosimilars became available -- for the three payer types were as follows:

• Medicare: 3.2%
• Medicaid: 5.2%
• Private: 1.8%

But from 2020 to 2022, after a third biosimilar was approved, mean annual increases ramped up:

• Medicare: 5.6%
• Medicaid: 13.0%
• Private: 16.4%

"By September 2022, uptake was higher for Medicaid (43.8%) and private insurance (38.5%) than Medicare (24%)," Roberts and colleagues wrote.

Data for the study came from the Rheumatology Informatics System for Effectiveness (RISE) registry, which collects patient-level data from some 1,100 U.S. rheumatology practices, representing about one-third of such practices in the country. Records for 37,560 individual patients receiving a total of 660,000 infliximab prescriptions were analyzed. About half were covered by Medicare, 43% by private insurance, and 5% by Medicaid.

"Originator" infliximab (Remicade) in 1998, initially for Crohn's disease and then for a host of other rheumatologic indications. After its patents expired and an approval process was established for biosimilars, infliximab-dyyb (Inflectra) was approved in 2016, followed the next year by . In late 2019, joined the list.

Roberts and colleagues speculated that the third biosimilar approval was crucial to the accelerated uptake seen in the later period. "Our results suggest that one or two biosimilars may not generate enough competition to speed adoption rates for biosimilars used to treat similar indications," they explained. Moreover, the sharp increase beginning in 2020 "is consistent with the removal of [formulary] exclusions after the difference in list prices between originator and biosimilar exceeds $15,000," as indicated by published last year.

One reason the researchers offered for Medicare's lag was that, until 2022, drugs administered under Part B (the norm for infusion drugs like infliximab) were reimbursed at 106% of the manufacturer's list price. Since originator infliximab was more expensive, "clinicians were not incentivized to offer lower cost products," the group argued.

In addition, they noted, Medicare Advantage plans were barred from requiring "step therapy" in which cheaper therapies must be tried first before the plan will pay for a more expensive alternative. Some relief might have been offered by a "temporary" policy Medicare implemented in 2022 to reimburse biosimilars at 108% of the list price, but this would not have been reflected in the current study's data.

Medicaid reimbursement, on the other hand, is controlled by individual states, where the funding mechanisms provide a clear incentive to prioritize the least expensive among multiple therapeutically equivalent options.

Uptake of biosimilars is vital to keep healthcare costs from soaring out of sight, the researchers suggested. "If biosimilars cannot gain an initial foothold, there is the theoretical risk that competition will decrease over time and the reduction in net price could disappear," they warned.

They called for "policies [that] incentivize the development and market entry of multiple biosimilars, streamline regulatory approval to reduce time to market, and encourage pricing strategies that promote competition."

"Additionally," they wrote, "policies could ensure transparent pricing and reimbursement practices, as well as educational initiatives to increase clinician and patient awareness and acceptance of biosimilars." Medicare in particular could do more to encourage use of biosimilars, the group said.

Limitations to the analysis included that academic centers are underrepresented in RISE, and infliximab prescriptions by non-rheumatology practices (such as gastroenterology and dermatology) would not have been included. The study also did not examine actual prices for originator or biosimilar infliximab to verify their potential to drive the study's findings.

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