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.