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P473. Infliximab is more immunogenic and reaches lower trough levels in ulcerative colitis patients compared to Crohn's disease patients

H. Bar-yoseph1, Y. Chowers1, S. Ben-Horin2, M. Waterman1, 1Rambam, Gastroenterology, Haifa, Israel, 2Shiba, Gastroenterology, Tel Hashomer, Israel

Background

Infliximab is effective for treating Crohn's disease (CD) and ulcerative colitis (UC). However, it is unknown if serum drug levels (SDL) and Infliximab antibody (ATI) formation differs between CD and UC patients.

Methods

SDL and ATI were prospectively determined in CD and UC patients on maintenance Infliximab therapy. Clinical outcomes were based on retrospective chart review. UC and CD patients (1:2 ratio) were matched for treatment (Infliximab dose & interval and percent of patients on combination therapy) and response. Mean SDL and ATI were compared using Chi-square test for categorical variables and Mann–Whitney test for continuous variables.

Results

Thirty-six responding patients (12 UC, 24 CD) were assessed. There was no difference between UC and CD groups in gender ratio, ethnicity, age at diagnosis, age at start of therapy, duration of therapy, disease duration prior to therapy, smoking status, treatment protocol and response to therapy. Mean ATI levels were significantly higher in the UC group compared with the CD group (10.34 and 1.48 mcg/ml, respectively, p = 0.029). ATI positivity (ATI >1 mcg/ml) was significantly more frequent in UC compared to CD (50% & 12.5%, respectively, p = 0.036). Mean SDL was 3.63 mcg/ml for UC and 4.32 mcg/ml for CD (p = 0.045) and 75% of UC patients had SDL ≤1 mcg/ml compared to 37.5% of CD patients (p = 0.038).

Conclusion

UC patients on maintenance infliximab therapy develop more ATI compared with CD patients. Serum infliximab levels associated with response to Infliximab maintenance are slightly lower in UC compared to CD. Larger cohorts are required to support these observations.