P417 Frequent Early Nocebo Complaints but Maintained Clinical Efficacy, Biomarker and Therapeutic drug levels following mandatory Biosimilar Switch in Patients with Inflammatory Bowel disease: Preliminary data from a Prospective Observational Cohort Study

Abstract Background Current evidence suggests that biosimilar is safe and effective for patients with IBD. There limited data on nocebo effect after switching from originator to biosimilar. We aimed report clinical efficacy, therapeutic drug monitoring, adverse events (AEs), frequency of in IBD switches. Methods performed a prospective observational study 257 consecutive who underwent switch at McGill University Health Centre, Montreal, Canada, between November 2021 October 2022. excluded 74 due missing follow-up data/delay the switch. Patients mandatory (Remicade or Humira) biosimilars change reimbursement policy Quebec. Clinical biochemical were captured 8 weeks before switch, baseline (time switch), 12 24 remission was defined as an HBI<5 Crohn's disease (CD) partial Mayo<3 points ulcerative colitis (UC). Biomarkers C-reactive protein (CRP<5mg/mL) fecal calprotectin (FCAL)<250 mcg/g. Drug trough levels anti-drug antibodies measured week (therapeutic level infliximab level≥3mcg/mL, adalimumab≥5mcg/mL). AEs effects assessed. Results A total 183 included [79.2% CD, male 57.4%, median age inclusion 46 years (IQR 30-52), duration 13 (IQR8-22)]. no significant difference proportion switch(88.5%), baseline(93.8%), 12(85.7%) 24(88.7%), p=0.835. Similarly, remaining biomarkers not significantly different baseline, 24; CRP (82.4%/75.0%/80.0%/77.3%), p=0.760; FCAL (76.7%/77.8%/71.2/77.3%), p=0.932, well there maintaining level, (85.5%/82.2%/79.6%, p=0.853) prevalence positive antibody (10.5%/4.4%/11.8%, p=0.190) 24, respectively. 14.5% had subtherapeutic levels, 6% dose optimization, 4.4% loss response/relapse. Nocebo reported 12% (9.3% within first 2.7% 5.5% AEs,and 3.8% discontinued AEs. Conclusion Despite number early complaints 3 months changes found antibodies.