P-066 A Search for the Best Utilization of Serum Infliximab and Antibodies to Infliximab Levels in Patients With Inflammatory Bowel Disease

Abstract

To perform a cross-sectional, observational study measuring IFX levels and ATI levels in patients with Ulcerative Colitis (UC) and Crohn’s Disease (CD) receiving IFX as maintenance therapy to determine correlations with response and utility in medical management. Patients with UC and CD who received IFX therapy at the infusion center were enrolled from 2011 to 2013. Five blood samples for measurement of serum IFX and ATI levels were obtained from the patient over 2 consecutive and between 2 infusions. Clinical data including diagnosis, disease extent, concurrent use of immunosuppressives, and allergic reactions to IFX were obtained. A global assessment of disease activity was assessed by personal interview and chart review and scored 0–4 (0 = clinical remission—4 = severe) at 3 time intervals (first infusion, mid-cycle, second infusion). Patients were stratified into 3 groups (disease->disease [DD], disease->remission [DR], remission->remission [RR]). A Wilcoxon Rank-Sum test was used to determine the statistical significance of median ATI and IFX concentration differences between the 3 patient groups. Thirty-eight patients (11 with UC, 27 with CD) were analyzed. There were no statistically significant differences found in serum IFX or ATI levels during any point amongst the 3 groups (DD = 18, DR = 10, RR = 10). Four (50%) of the 8 patients not on concurrent immunosuppressives were ATI+ compared to 7 (23%) of the 30 patients on concurrent immunosuppressives. Five patients (13%) had allergic reactions to IFX, and 2 were ATI+. A subgroup analysis of 18 patients (47%) was performed on patients with IFX trough (<3 µg/mL) at initial blood draw of the first infusion, none of whom were dose escalated based on clinical judgment; 14 (78%) had clinical improvement or maintained remission and 4 (22%) did not. We have studied 38 patients receiving IFX maintenance therapy who showed no significant difference in serum IFX and ATI levels despite variable disease activity over an 8–12 week follow up. Neither “sub-therapeutic” drug levels nor the presence of ATI precluded the maintenance of remission or clinical improvement. Dose titration based on drug level does not appear to be a more effective strategy than management by clinical judgment among all patients on ongoing therapy. In cases of loss of response, allergic reaction, or dose escalation when there is already a high level of IFX, availability of drug levels may be useful and we reserve our final conclusions until the results of larger trials are reported.