Introduction Maintenance infliximab (IFX) is established as treatment for Crohn’s Disease (CD) and ulcerative colitis (UC). Efficacy is improved with regular dosing to reduce antibody (Ab) development, though antibodies may anyway develop. The optimal time to stop IFX in remission is unknown: there is no reliable guidance to indicate who will relapse. Patients may be reluctant to stop treatment which has served them well despite significant risks and costs in continuing ineffective treatment. The measurement of IFX drug and Ab levels may help decision-making. Undetectable trough drug levels and high antibody levels (IFX-Ab) may suggest ineffective treatment and support stopping IFX in those in remission. Our centre has measured IFX drug and Ab since Sept 2015. We present how this has influenced patient management.
Methods We studied 80 IBD patients (55 CD/25 UC) receiving regular IFX to maintain remission. IFX trough drug levels and IFX-Ab levels were measured in all patients between Sept and Dec 2015. Samples were analysed at Exeter Clinical Laboratory International. Disease activity was assessed by the Harvey-Bradshaw Index (HBI) at time of last infusion and the most recent faecal calprotectin was recorded for each patient
Results IFX was given at a median interval of 2 months (range 1–3 months) for a median of 29 months (range 5–130). 39 out of 80 had immunosuppression with azathioprine/6 MP or methotrexate when levels were measured. Eighteen (13 Crohn’s/5 UC) of 80 patients had no detectable IFX in the presence of IFX-Ab (median 328 AU/ml range 12 to >500). This group had a similar duration of treatment (median 25 months range 8–89 months) but were less likely to be on immunosuppressant medication (4/18). Of these 18, 2 were clinically relapsing. The remaining 16 appeared in remission or minimally active (HBI median 1.5, range 0–6 a patient with bile-salt diarrhoea excluded), the median faecal calprotectin levels was 72 µg/g (range <30 to 249) a median of 4 months from measured IFX levels. Results were discussed with patients and the decision made to stop IFX treatment. Immunosuppressant medication was started as appropriate. A further 18 patients had IFX-Ab in the presence of a measurable trough drug level
Conclusion In 80 IBD patients on maintenance IFX, 16 (20%) had no detectable IFX trough levels but significant levels of IFX-Ab whilst in remission. Routine measurement of IFX levels and Ab as part of routine clinical practice may identify patients receiving no benefit from maintenance therapy, reducing costs, risks and treatment burden. Ongoing study is necessary to determine outcomes of patients stopping biologics and of patients in whom infliximab levels and infliximab antibodies co-exist
Disclosure of Interest None Declared
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