Background Anti-TNFa therapies have improved response rates in inflammatory bowel disease. However primary loss of response is problematic.

Aim Aim of this study was to explore relationship between infliximab (IFX) and adalimumab (ADA) trough and antibody levels with clinical response.

Method This was a prospective, single centre study. Patients were recruited from July 2015-August 2016. Inclusion criteria were patients older than 17 years with IBD who started treatment with anti-TNFa drugs (infliximab/adalimumab) Patient demographics, clinical history were collected from electronic records. Clinical disease activity indexes were performed (Harvey-Bradshaw Index for Crohn’s disease (CD), and partial Mayo scores for Ulcerative colitis (UC)). Clinical response defined as reduction in HBI≤3 or reduction in partial Mayo score ≤4 and <30% from baseline. Anti-TNFa trough and antibody levels were measured using ELISA.

Results 35 patients were recruited; 23 CD, 12 UC. 18 patients treated with ADA, 17 IFX. Mean age 40.3 years, 62.9% female, 34.3% thiopurines, 25.7% prior anti-TNFa exposure. Response rate 51.4%, 33.3% for ADA, 70.6% for IFX. Overall trough levels were 12.5 ug/ml for IFX, 4.4 ug/ml for ADA. There was clear link between higher anti-TNFa trough levels at induction with clinical response. For infliximab, mean trough levels in responders were 16.4 ug/ml (IQR 8.4-22.7) versus 5.3 ug/ml(IQR 0.5–8.8) for non-responders (p value 0.02 95% CI: 1.5 to 20.7). Similarly there was a link between higher ADA levels with clinical response, though not statistically significant. Responders mean trough 6.6 ug/ml versus non-responders 3.0 ug/ml (p value 0.14). Antibody formation occurred in 28.5%.

Conclusions Higher anti-TNFa trough levels at induction are associated with improved clinical response.