962 Clinical Utility of Measuring Infliximab and Human Anti-Chimeric Antibody Levels in Patients with Inflammatory Bowel Disease

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<ul><li><p>962</p><p>Clinical Utility of Measuring Infliximab and Human Anti-Chimeric AntibodyLevels in Patients with Inflammatory Bowel DiseaseWaqqas Afif, Edward V. Loftus, William A. Faubion, Karen A. Hanson, William J.Sandborn</p><p>Background: Treatment with infliximab (IFX) can result in immunogenicity through theformation of human anti-chimeric antibodies (HACAs). These antibodies are associated witha decreased duration of response, whereas therapeutic levels of IFX are associated withdurable clinical response. We evaluated the clinical utility of measuring serum IFX andHACA levels. Methods: We retrospectively reviewed charts of patients with inflammatorybowel disease who had IFX drug and HACA levels measured over a three-year period from2005-2008. The clinical utility of these tests was assessed by determining whether theresult affected clinical management. The management and subsequent clinical response totherapeutic changes based on test results was evaluated. Fisher's exact test and log-rank testfor discontinuation were used for statistical analysis. Results: One hundred and fifty-fivepatients underwent IFX level and HACA status testing. The median time to initial testingafter IFX initiation was 50 weeks (IQR: 22.7-120). The main indications for testing were:loss of response to IFX (50.3%), partial response after initiation of IFX (22.6%) and possibleautoimmune/delayed hypersensitivity reaction (14.8%). HACAs were identified in 35 patients(22.6%) and therapeutic IFX levels were found in 51 (32.9%). Of 177 total tests assessed,the results impacted treatment decisions in 73.4% (95% CI: 66-80%). In those with positiveHACAs, change to another anti-TNF was associated with a complete or partial response in91.6% of patients whereas increasing the dose had a response of 16.7% (p</p></li></ul>


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