Background & Aims: Antibodies to infliximab reduce serum infliximab with loss of clinical benefit, but undetectable trough serum concentrations of infliximab may occur without antibody formation. The relation between trough serum infliximab and clinical outcomes was evaluated in acute ulcerative colitis.
Methods: In a cohort of 115 ulcerative colitis patients treated with 3-dose induction followed by scheduled maintenance infliximab, rates of clinical remission, colectomy, antibodies to infliximab and trough serum infliximab were determined.
Results: Rates of remission were 32% at week 10 and 37% at week 54. Colectomy occurred in 40% of patients, at a median of 5.3 (IQR: 1.9-12.1) months. Detectable trough serum infliximab was present in 39% of patients and among patients with undetectable infliximab, 41% were antibody positive and 20% were antibody negative. For antibody positive and antibody negative patients, rates of remission (18% vs. 14%), endoscopic improvement (25% vs. 35%) and colectomy (52% vs. 59%) were not different. A detectable serum infliximab was associated with higher rates of remission (69% vs. 15%; P <0.001) and endoscopic improvement (76% vs. 28%, P <0.001). An undetectable serum infliximab predicted an increased risk for colectomy (55% vs. 7%, odds ratio 9.3; 95% confidence interval, 2.9 - 29.9; P <0.001). Concurrent immunosuppression was not associated with clinical outcomes.
Conclusions: For ulcerative colitis patients treated with infliximab, a detectable trough serum infliximab predicts clinical remission, endoscopic improvement, and a lower risk for colectomy. In assessing clinical outcomes to infliximab, the presence of antibodies to infliximab is a surrogate for absent drug.