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Background Anti-TNF therapy is recommended as a treatment for patients with Crohn ́s perianal fistulas. However, a significant proportion of patients have a sub-optimal response to anti-TNF therapy. Higher serum levels of anti-TNF agents have been associated with improved outcomes in perianal Crohn’s disease. Currently, it is unknown whether anti-TNF agent levels can be detected in tissue from fistula tracts themselves and whether this is associated with response. Methods We undertook a pilot study to develop a method to measure fistula tissue levels of anti-TNF medication (infliximab and adalimumab) using a targeted proteomic technique that employs ‘signature peptide detection’ following trypsin digestion called ultraperformance liquid chromatography–mass spectrometry (UPLC-MS), to quantify a protein. The targeted UPLC- MS/MS detection and quantification method implemented were previously validated. Biopsies were obtained from patients with Crohn’s disease who underwent an examination under anaesthesia for worsening fistula symptoms despite maintenance anti-TNF therapy. Idiopathic (cryptoglandular) tissues from purposively sampled matched (age/gender) patients were analysed as negative controls and these samples were spiked with anti-TNF drugs as positive controls. Results Tissue was sampled from the fistula tracts of seven patients with Crohn’s perianal disease (5 patients were on adalimumab and 2 patients were on infliximab). The limit of detection (LOD) and linearity range of the method was assessed for each drug in the spiked idiopathic fistula samples. Infliximab and adalimumab had a LOD of 0.004 and 2 μg/ml respectively with linearity demonstrated for both drugs. The anti-TNF drugs, infliximab and adalimumab, were not detected in fistula samples from any of the Crohn’s patients despite detection in ‘spiked’ positive control samples. In addition, to validate the result, samples were concentrated (x10) and still there was no detection of the drugs in the test samples. Conclusion The anti-TNF drugs adalimumab and infliximab were not detected in fistula biopsy samples from patients with Crohn ́s perianal fistulas with refractory symptoms despite maintenance therapy. This raises the question on the role of tissue penetrance of anti-TNF drugs in response to therapy. Further work is required in a larger number of patients to validate the findings observed and investigate whether any correlation exists between tissue and serum levels of anti-TNF and clinical outcome.

P345 Lack of anti-TNF drugs levels in fistula tissue: A reason for non-response in Crohn’s perianal fistula?