Hiroaki Mamiya, Toshiki Fukasawa, Koji Kawakami
8 min
Abstract
Background Biosimilars present a significant opportunity for cost savings. However, the uptake of biosimilars has been inconsistent across different regions and drugs, highlighting the need for effective policy interventions. This study aimed to investigate the impact of Japan's reimbursement incentive policy on the utilisation of etanercept and infliximab biosimilars among patients with rheumatoid arthritis.Methods We conducted an interrupted time-series (ITS) analysis using data extracted from the JMDC claims database in Japan. Participants included those prescribed either the brand-name biologics or their biosimilars. The primary outcome was the proportional use of biosimilars relative to the total use of both biosimilars and originator drugs.Results The ITS analysis demonstrated varied responses to the reimbursement policy across the two biosimilars. For infliximab, although the policy did not result in a significant level change (0.14%; 95% confidence interval [CI]: −2.83, 3.11), there was a positive but nonsignificant slope change of 0.21% per month (95% CI: −0.13, 0.55). In contrast, for etanercept, the policy led to a significant level change, with an immediate increase in use by 13.48% (95% CI: 7.82, 19.14). However, the slope change showed a significant decrease by −1.09% per month (95% CI: −1.50, −0.68).Conclusion The results indicate that while the reimbursement policy was associated with a short-term increase in the uptake of etanercept biosimilars, it had limited impact on infliximab biosimilars. This variation suggests that financial incentives alone may not be sufficient to enhance biosimilar adoption and that policies must consider drug-specific and healthcare setting-specific factors.
Sam: Yes. For etanercept, the biosimilar matches all the uses of the original drug, and patients can inject it themselves under the skin at home, using a simple device like an auto-injector pen—much like giving yourself insulin if you have diabetes. That makes switching straightforward for doctors in outpatient clinics. In contrast, infliximab requires an intravenous infusion, where the drug drips directly into a vein through a needle over an hour or more in a clinic setting. The extra time, staff, and equipment make it a heavier burden, even with the small premium.
Alex: Okay, so self-injection removes a big hassle for etanercept, but clinics still have to handle the full infusion process for infliximab... that outweighs a $10 bonus?
Sam: Precisely. The study excluded cases where infliximab's original version treats unique conditions like certain inflammatory diseases, ensuring a fair comparison on rheumatoid arthritis claims. Despite that, clinics stuck with the originator for infliximab—the policy triggered no meaningful change there.
Alex: Huh... so the ease of use tipped the scale for one but not the other. And that immediate jump suggests the incentive worked when the path was clear.
Sam: The paper suggests this saved Japan around $6.7 million on etanercept alone by boosting cheaper options where practical. It underscores that policies need to account for these practical differences—like administration burden—to succeed, rather than applying a one-size-fits-all bonus.
Alex: But how did they measure that immediate jump so precisely, without just guessing from overall trends?
Sam: They looked closely at two key shifts in the monthly data. First, there's the sudden step up right when the policy hit—like a car suddenly accelerating from a stoplight after months of steady driving. That's the level change, an immediate shift in the proportion of biosimilar use. For etanercept, it showed a substantial jump, statistically reliable. Second, they checked if the ongoing trend sped up, slowed, or stayed the same afterward. Etanercept's growth, already climbing briskly before, dropped after, suggesting the quick boost tapered off. For infliximab, neither shift was meaningful.
Alex: So for etanercept, the policy gave a clear one-time push, but didn't keep the momentum going as fast... unlike a steady climb.
Sam: Exactly. The paper points to a few reasons for that slowdown. Biosimilar adoption was already picking up speed before the policy, so the incentive might have just accelerated what was coming anyway. Then there's a possible ceiling effect—once easier switches happened, fewer willing doctors or patients remained. Plus, the premium only applies to three claims per patient, limiting long-term pull.
Alex: Huh, that three-claim limit makes sense as a built-in brake... and with only a year of post-data, they call it preliminary?
Sam: Yes, the follow-up period was just 12 months, so long-term patterns need more time to confirm. They ran sensitivity checks with different ways to handle data patterns, like adjusting for monthly ups and downs, and the main findings held steady for both drugs.
Alex: Right... so the real lesson is matching incentives to each drug's real-world fit, not assuming one bonus fixes everything.
Sam: Approved uses for a drug—what conditions doctors are officially allowed to prescribe it for—can differ between the original and its copy. For infliximab, the copies miss some approvals the original has, like for Behçet's disease, a rare condition causing widespread inflammation in blood vessels and tissues. Hospitals often stock only the original to cover all possible patients. Etanercept's copies match the original's approvals almost exactly, so no such restriction holds doctors back.
Alex: Huh... so that alone could tip hospital stockrooms toward the pricier original for infliximab, even with the bonus.
Sam: Another factor is how easily patients or doctors can switch back if issues arise. Etanercept goes under the skin weekly with a simple shot anyone can learn at home, like using an EpiPen for allergies. If something feels off, grabbing the original is quick—no big hassle. Infliximab's vein drip every eight weeks ties up clinic time and gear for an hour, making reversals a chore that discourages trying the copy.
Alex: Right, that operational drag on clinics makes the $10 feel trivial... especially since both are outpatient drugs.
Sam: The modest premium can get undercut by original makers' tactics, like secret volume discounts or rebates to hospitals—common strategies we can't see in claims data, but consistent with past reviews. The paper notes these market moves and drug maturity differences as untested ideas explaining why etanercept responded but infliximab didn't.
Alex: Those lessons sound practical for tweaking policies... but like any study, this one has limits we should consider.
Sam: Yes, a few important ones. The database mainly tracks working-age people under 75 and their families, so it misses older rheumatoid arthritis patients—who often have more health issues and might react differently to money incentives. Also, they only had data up to early 2023, giving just 12 months after the policy for infliximab—that short window might hide slower or longer-term shifts.
Alex: Right, so the elderly gap and quick snapshot make sense as cautions... especially since older folks deal with more complications.
Sam: Exactly. Without a direct comparison group—like another drug unaffected by the policy—it's harder to pin changes solely on the incentive, though the month-by-month trends help control for natural drifts. Overall, the findings fit Japan's setup and may not transfer directly elsewhere.
Alex: Makes sense... a reminder that one-size-fits-all fixes rarely stick in medicine. This study lays out why, grounded in real prescriptions.
Sam: Precisely. It's a clear case for policies that adapt to practical hurdles, offering useful insights for Japan and beyond.
Alex: That's our look at how drug differences shaped a Japanese incentive's success on arthritis treatments. Thanks for joining ResearchPod.