Real-World Patterns of Immunomodulator Use in Patients with Inflammatory Bowel Disease Receiving Biologic Therapy Under a 54-Week Reimbursement Cap: A 12-Year Retrospective Single-Center Cohort from Taiwan.

Background: Recent studies have shown that concomitant immunomodulator (IMM) use does not significantly affect remission in patients with inflammatory bowel disease (IBD) treated with non-anti-tumor necrosis factor (non-anti-TNF) biologics. We evaluated the real-world role of IMMs in IBD patients receiving biologic therapy, including potential use as bridge therapy - continuing IMMs to maintain remission during mandated biologic treatment intervals - and patterns of IMM withdrawal and reinitiation. Materials and Methods: This retrospective, single-center study included IBD patients receiving biologic therapy from May 2013 to April 2025 under Taiwan's National Health Insurance policy, which imposes a 54-week biologic reimbursement cap and mandatory drug-free interval. The biologic course was the unit of analysis; within-patient clustering was addressed using generalized estimating equations (GEE). Results: In total, 144 patients (71 Crohn's disease [CD], 73 ulcerative colitis [UC]) contributed 280 courses (150 CD, 130 UC). Concomitant IMM use was similar between CD and UC (OR 1.06, 95% CI 0.59-1.89; p = 0.846); longer disease duration was independently associated with lower odds of IMM use (OR 0.92, 95% CI 0.87-0.97; p = 0.002). Remission (75.4% vs 74.3%), IMM withdrawal (32.8% vs 20.0%), and safety event rates did not differ significantly between groups (all p > 0.05). Among patients on non-anti-TNF biologics, IMM withdrawal was significantly more frequent in UC than CD (24.6% vs 7.1%; OR 0.25, 95% CI 0.08-0.84; p = 0.025), while IMM reinitiation after biologic withdrawal was significantly less common in UC than CD (40.0% vs 85.7%; OR 7.97, 95% CI 1.31-48.67; p = 0.025). In UC, annual trends in anti-TNF- and non-anti-TNF-based combination therapy were individually non-significant, though non-anti-TNF-based therapy predominated overall (p = 0.005). In CD, the increasing trend in non-anti-TNF-based combination therapy reached borderline significance (p = 0.052), while the overall difference between strategies remained non-significant. IMM withdrawal increased significantly over time in UC (p = 0.010) but not in CD (p = 0.059). Conclusion: IMM use, remission, and safety outcomes were similar between UC and CD, but IMM withdrawal and reinitiation patterns after biologic treatment intervals differed significantly by disease type. These findings describe current practice patterns under Taiwan's reimbursement constraints rather than a causal bridge-therapy role for IMMs; prospective, comparator-controlled studies are warranted.