P537 Is anti-TNF therapeutic drug monitoring of value in IBD patients in clinical remission?

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Background: Therapeutic drug monitoring (TDM) and the concept of treat-to-target are yielding better outcomes in patients with inflammatory bowel disease (IBD). Serum levels of anti-TNF therapy are associated with clinical response and mucosal healing. This study aims to evaluate the association between serum levels of anti-TNF therapy and faecal calprotectin, disease activity scores, endoscopic findings and biochemical markers in IBD patients.

Methods: Serum drug levels were measured in patients presenting between 2014-August 2016. Demographic information and clinical characteristics were retrieved retrospectively from medical records. Disease activity scores (CDAI, Mayo), endoscopic findings, biochemical data (CRP, platelet, albumin) and faecal calprotectin levels were obtained close to the time of serum levels of anti-TNF therapy. Patients with sub-therapeutic and therapeutic serum levels of anti-TNF therapy were compared using Fisher exact tests. Simple linear regression was performed to correlate CRP, platelet and albumin levels with anti-TNF levels.

Results: The 67 patients with available serum levels were included. Patients had a mean age of 34 years (SD =18.5) and 60% were female. The majority (79%) had Crohn's disease and 82% were on maintenance infliximab. 41 (61%) patients had sub-therapeutic drug levels.

All 17 (100%) of those with therapeutic levels on maintenance therapy were in clinical remission (CDAI score <150 or partial Mayo score of <2). All 7 (100%) of those in clinical relapse had sub-therapeutic levels but in contrast, most patients {29/52 (56%)} who were in clinical remission did not have therapeutic levels of anti-TNF agents (p=0.036).

14/15 (93%) of those with sub-therapeutic levels and 4/9 (44%) with therapeutic levels on maintenance therapy had elevated faecal calprotectin (FC >50 mg/kg) whilst 5/6 (83.3%) patients who had normal faecal calprotectin and 4/18 (22%) of patients who had elevated faecal calprotectin had therapeutic levels (p=0.015).

There was no difference with respect to endoscopic activity and anti TNF levels although there was a significant trend (p=0.051). Platelet levels correlated with anti TNF levels (simple linear regression; p=0.042) but there were no differences with respect to CRP and albumin levels.

Conclusions: In the presence of clinical remission and/or a normal faecal calprotectin assay, TDM is unlikely to alter management. “Therapeutic” trough levels for patients in clinical remission may differ from those with active disease. Further data is required to confirm these findings.

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