Anti-tumor necrosis factor alpha (TNFα) therapies have improved outcomes for patients with inflammatory bowel disease. The aim of this study was to explore the relationship between infliximab (IFX) and adalimumab (ADL) trough and antibody levels with clinical response rates at the end of induction.
This was a prospective, single-center study. Patients were recruited from July 2015 to August 2016. Inclusion criteria were all inflammatory bowel disease patients older than 17 years who started treatment with IFX or ADL. Baseline clinical disease activity indexes were performed. Clinical response was defined as HBI ≤3 or partial Mayo score ≤4% or <30% reduction from baseline. Anti-TNFα trough and antibody levels were measured using standard ELISA techniques.
Thirty-five patients were recruited, of whom 23 had Crohn's disease and 12 had ulcerative colitis. Eighteen were treated with ADL and 17 with IFX. The mean age of the cohort was 40.3 years, 62.9% were females, 34.3% were on concomitant thiopurines, and 25.7% had prior anti-TNFα exposure. Overall response rate was 51.4%, 33.3% for ADL and 70.6% for IFX.Mean trough levels were 12.5 μg/mL for IFX and 4.4 μg/mL for ADL. There was a clear link between higher anti-TNFα trough levels at the end of induction with clinical response rates. For IFX, mean trough level was 16.4 μg/mL for responders 
Higher trough levels at the end of induction are associated with improved response. Ongoing work will define optimal targets at this key timeframe.