Is It Useful to Monitor Thiopurine Metabolites in Pediatric Patients with Crohn's Disease on Combination Therapy? A Multicenter Prospective Observational Study.

BACKGROUND: The additional value of azathioprine concomitant treatment on infliximab pharmacokinetics in children is not well described yet. AIMS: In the present study, we aimed to describe the relationship between thiopurine metabolite levels, infliximab trough levels, anti-IFX antibody formation, and clinical and laboratory markers of disease activity in pediatric patients with Crohn's disease, and to assess non-adherence. METHODS: Data were collected prospectively during repeated visits from pediatric patients followed for Crohn's disease in two Czech pediatric inflammatory bowel disease centers between January 2016 and June 2017. Thiopurine metabolites (6-thioguanine and 6-methylmercaptopurine) were measured by high-performance liquid chromatography. Infliximab trough levels and anti-IFX antibody serum levels were measured routinely by ELISA. The risk of loss of response to infliximab therapy was also assessed. RESULTS: A significant association between infliximab serum levels and 6-thioguanine erythrocyte levels was observed when tested as categorical variables (63 patients, 321 observations). To predict infliximab levels > 5 µg/mL, we propose a 6-thioguanine cutoff of 278 pmol/8 × 108 erythrocytes (sensitivity, 0.799; specificity, 0.347). A higher loss-of-response-to-infliximab rate (tested in a subgroup of 51 patients) was observed in patients with undetectable 6-thioguanine levels than in those with detectable levels (p = 0.026). Non-adherence to azathioprine therapy was suspected in 20% of patients. CONCLUSION: Thiopurine metabolite monitoring in pediatric patients with Crohn's disease is useful when optimizing combination therapy. Pediatric patients with undetectable 6-thioguanine levels are more likely to lose response to infliximab therapy. When targeting optimal infliximab levels, the 6-thioguanine cutoff levels in children appear to be higher than in adults.

Fecal zonulin is elevated in Crohn's disease and in cigarette smokers.

OBJECTIVES: Human zonulin is a protein that increases permeability in the epithelial layer of the small intestine by reversibly modulating the intercellular tight junctions. There is not sufficient information available about zonulin's participation in inflammatory bowel diseases (IBD). The aim of this study was therefore to investigate fecal and serum zonulin in IBD patients and its relation to the disease localization, behavior and smoking status. DESIGN AND METHODS: Forty IBD patients and forty healthy persons were examined for fecal and serum zonulin concentrations by competitive ELISA (DRG International Inc). Values were correlated to IBD type, localization and behavior, and smoking. RESULTS: Serum and fecal zonulin were significantly higher in patients with Crohn's disease compared to ulcerative colitis (p = 0.038 for fecal zonulin, and p = 0.041 for serum zonulin concentrations). No association of serum or fecal zonulin was found with respect to IBD localization and behavior. The only difference was found with respect to smoking. Both the IBD cohort and healthy smokers showed significantly higher fecal zonulin levels (median 203 ng/mL) compared to non-smokers (median 35.8 ng/mL), p < 0.001. CONCLUSIONS: Fecal and serum zonulin levels are elevated in patients with active Crohn's disease but not with ulcerative colitis. High fecal zonulin levels in smokers irrespective of IBD point to the significant and undesirable up-regulation of gut permeability in cigarette smokers.