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Aims: Therapeutic drug monitoring (TDM) of infliximab (IFX) appears to be beneficial for patients with inflammatory bowel disease (IBD). However, the recommended target concentrations depend partly on the method used to quantify IFX. Since we recently developed a liquid chromatography-tandem mass spectrometry method to quantify IFX, we aimed to determine IFX trough concentrations (Cmin) associated with biological remission., Methods: We retrospectively measured IFX Cmin in sera from 55 patients with IBD, on IFX maintenance therapy, and for whom demographic, biological and clinical data were collected from medical records. A threshold of IFX Cmin associated with biological remission (defined by C-reactive protein < 5 mg l -1 and faecal calprotectin <150 μg g -1 ) was determined using receiver operating characteristics analysis., Results: IFX Cmin ranged from <1 mg l -1 to 57.2 mg l -1 . IFX Cmin were higher (P = 0.038) in patients with biological remission and a cut-off of IFX Cmin set to 6.2 mg l -1 was associated with biological remission (sensitivity = 0.75, 95% confidence interval 0.58-0.75; specificity = 0.61, 95% confidence interval 0.39-0.83)., Conclusion: Liquid chromatography-tandem mass spectrometry measurement of IFX Cmin and the determination of a new threshold of IFX Cmin associated with biological remission are new steps towards IFX treatment personalization in patients with IBD., (© 2018 The British Pharmacological Society.)