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P426 Supra-therapeutic infliximab levels are not associated with a higher risk of infection in IBD patients

Greener T.*1, Kabakchiev B.2, Silverberg M.3

1Mount Sinai Hospital, Department of Gastroenterology, Toronto, Canada 2Mount Sinai Hospital, Joseph and Wolf Lebovic Health Complex Zane Cohen Centre for, Toronto, Canada 3University of Toronto, Gastroenterology Division, Toronto, Canada


Anti-TNF agents are associated with an increased risk of infection. Data evaluating the relationship between infliximab (IFX) concentration and toxicity are limited. The aim of this study was to evaluate the frequency of adverse events (AEs) in IBD patients with supra-therapeutic (ST) IFX levels compared to those with “normal” range (NR) levels.


We performed a retrospective analysis of 180 patients with at least one measurement of serum IFX using a homogenous mobility shift assay (HMSA) assay (Prometheus Laboratories) from November 2012 through June 2016. The cohort was divided according to an IFX level cut-off of 15 μg/ml (ST and NR) levels). Frequencies of AEs including infections, skin manifestations and infusion reactions were compared between the 2 groups. A similar analysis was performed after dividing the patient cohort into 3 subgroups according to levels (<8/8–20/ >20). An “intra-individual” case series analysis was also performed comparing infection rates in patients with 2 reported levels, one in each range (NR and ST). Multivariate logistic regression was applied to assess factors associated with an increased risk for infection


Patients with ST levels did not have an increased rate of infections in comparison to patients with NR levels (12% vs 19%; p=0.3). Serious infections, opportunistic infections and skin manifestations were also similar between the 2 groups. Using the 3 subgroups determined by levels, infection rates were still comparable. Total AEs and infusion reactions were found to be significantly more common in the NR cohort (42% vs 21%; p<0.01 and 10% vs 1%; p<0.01, respectively). For the “intra-individual” analysis with 2 measured levels in the same subject, higher levels were not associated with an increased risk of infection. Disease activity, concomitant immunosuppression and steroids were not significantly associated with rates of infection.

Table 1. Demographic and clinical characteristics of patients with IFX levels lesser or greater than 15 μg/ml

Table 2. Adverse effects in patient with lesser and greater levels than 15 μg/ml


This is the first study to directly compare rates of infection in IBD patients exposed to high and NR levels of IFX. Higher IFX serum concentrations were not associated with higher rates of infections, even in patients exposed to very high levels. Clinicians and patients should be aware of the risks of AEs with IFX therapy but higher levels do not appear be associated with a higher than expected rate of adverse events.