PWE-014 The impact of therapeutic drug monitoring during biosimilar infliximab switch in inflammatory bowel disease

Introduction Therapeutic Drug and antibody monitoring (TDM) is now an established strategy to manage patients with Inflammatory Bowel disease being treated with Biologic agents. Biosimilar switching of Originator Infliximab (IFX) is recommended by ECCO and BSG. The role of TDM during biosimilar infliximab switch is not well studied. This study aimed to analyse and compare IFX drug and antibody levels before and after switch. Aims To study the impact of TDM on Biosilimar infliximab switching by detecting the proportion of patients who have sub-therapeutic drug levels and/or anti-IFX antibodies either before or 3 months after the switch, who would be considered as secondary loss of response (LOR). Methods All patients with either Crohn’s disease (CD) or Ulcerative Colitis(UC) who were switched to Remsima, a biosimilar Infliximab in 2017 at the two hospital sites were included. Disease activity was assessed using Harvey-Bradshaw Index (HBI) or Simple Clinical Colitis Activity Index(SCAI). The most recent colonoscopy/radiological imaging and faecal calprotectin (FCP) was recorded. Pre and post- switch Infliximab and antibody levels were obtained. Concomitant use of immunomodulators (Azathioprine, Mercaptopurine or Methotrexate) was noted. Results 119 patients had IFX Remicade switch to Biosimilar Inflectra or Remsima. 86 pts had CD and 32 had UC. 110 patients had pre-switch therapeutic drug and antibody monitoring, and 115 had post switch monitoring as well within 3 months. 67 pts had sub-therapeutic but detectable IFX drug levels prior to the switch with either mild or inactive clinical scores for both CD and UC. 19 patients had undetectable IFX drug levels, and post switch continued to have undetectable levels. 16 of these 19 patients had high anti-IFX antibodies suggesting that these patients were secondary loss of response who needed a change of their biologic to another agent. 11/86 patients had dose escalation to 10 mg/kg and then attained therapeutic levels. SCAI ranged between 0–9, mean 1.433, and HBI ranged between 0–12, mean 2, indicating that majority of patients were in remission. Post switch matched FCP showed 60 pts in remission with FCP 250 ug/g. Conclusions Therapeutic drug and antibody monitoring before and 3 months after Biosimilar switch detects secondary loss of response in patients maintained on scheduled IFX treatment in clinical and biochemical remission. It should be recommended over blanket switching as it may prevent un-necessary switching for some patients who are no longer responding the IFX or those who may merit a drug withdrawal.