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* = Presenting author

P507 Clinical role, optimal timing and frequency of measurement of serum infliximab levels and anti-infliximab antibody titres in patients with inflammatory bowel disease

R. Bor*1, K. Farkas1, A. Bálint1, A. Milassin1, M. Rutka1, M. Matuz2, F. Nagy1, A. Fábián1, Z. Szepes1, T. Molnar1

1University of Szeged, First Department of Medicine, Szeged, Hungary, 2University of Szeged, Faculty of Pharmacy, Szeged, Hungary

Background

The introduction of biological treatment has made a major breakthrough in the management of inflammatory bowel disease (IBD). However, a substantial number of patients show only partial response, and, in approximately 40% of initially responders, it loses its effect. The cessation of therapy or the switching to another biological drug currently depends mainly on the clinical judgement. Serum infliximab (IFX) and anti-infliximab antibody (ATI) levels are objective parameters that may have a great role in the therapeutic decisions, but the optimal timing and frequency of their measurements are still not clearly defined.

Methods

Our aim was to assess the optimal timing and frequency of sampling for measurement of serum IFX and ATI levels during biological therapy. In total, 48 IBD patients receiving maintenance IFX therapy were prospectively enrolled: 20 patients were in complete remission (responder group), and 28 patients showed inadequate response including partial and loss of response or the need for dose escalation. Blood samples were collected before and 2 and 6 weeks after the administration of IFX. We examined the correlation between these parameters and the present clinical and the long-term response.

Results

Our results confirmed that the expression of ATI in the circulation is transient. Using the 3-points measurements, ATI expression showed significant difference between the responder and inadequate responder group (5.0% vs 35.7%; p = 0.016); however, single sampling of the ATI was insufficient for predicting therapeutic response. In the inadequate responder group ATI expression were detected in 10 cases; however, 4 patients showed appropriate long-term response. The mean value of week 0 serum IFX levels were significantly higher in the responder group (3.11 ± 1.64 vs 1.19 ± 1.11; p < 0.001) compared with the inadequate responders without further difference on the second and sixth week. In addition, 70.8% of patients could have been categorised correctly based on the cut-off value of serum IFX level of 2.281 µg/ml at week 0. On the long-term follow-up, 4 patients in the inadequate responder group with initially low serum IFX level responded. However, 2 patients in the inadequate responder group with high serum IFX level lost response on the follow-up.

Conclusion

Our results suggest that the simultaneous measurement of serum IFX levels and ATI titres not only at week 0 but also at week 2 and week 6 after the administration, significantly increase the diagnostic accuracy for the therapeutic decision in uncertainly responded patients and can serve as a highly precise tool for the evaluation of therapeutic response in the questionable situations.