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.

• MeSH
• azathioprin terapeutické užití   MeSH
• biologické markery MeSH
• Crohnova nemoc farmakoterapie   MeSH
• dítě MeSH
• imunologické faktory terapeutické užití   MeSH
• infliximab terapeutické užití   MeSH
• kombinovaná farmakoterapie MeSH
• lidé MeSH
• longitudinální studie MeSH
• merkaptopurin analogy a deriváty   analýza   MeSH
• mladiství MeSH
• prospektivní studie MeSH
• Check Tag
• dítě MeSH
• lidé MeSH
• mladiství MeSH
• mužské pohlaví MeSH
• ženské pohlaví MeSH
• Publikační typ
• časopisecké články MeSH
• multicentrická studie MeSH
• pozorovací studie MeSH
• Názvy látek
• 6-methylthiopurine MeSH Prohlížeč
• azathioprin MeSH
• biologické markery MeSH
• imunologické faktory MeSH
• infliximab MeSH
• merkaptopurin MeSH

Infliximab (IFX) is administered intravenously using weight-based dosing (5 mg/kg) in inflammatory bowel disease (IBD) patients. Our hypothesis is that especially young children need a more intensive treatment regimen than the current weight-based dose administration. We aimed to assess IFX pharmacokinetics (PK), based on existing therapeutic drug monitoring (TDM) data in IBD patients < 10 years. TDM data were collected retrospectively in 14 centres. Children treated with IFX were included if IFX was started as IBD treatment at age < 10 years (young patients, YP) and PK data were available. Older IBD patients aged 10-18 years were used as controls (older patients, OP). Two hundred and fifteen paediatric inflammatory bowel disease (PIBD) patients were eligible for the study (110 < 10 year; 105 ≥ 10 years). Median age was 8.3 years (IQR 6.9-8.9) in YP compared with 14.3 years (IQR 12.8-15.6) in OP at the start of IFX. At the start of maintenance treatment, 72% of YP had trough levels below therapeutic range (< 5.4 μg/mL). After 1 year of scheduled IFX maintenance treatment, YP required a significantly higher dose per 8 weeks compared with OP (YP; 9.0 mg/kg (IQR 5.0-12.9) vs. OP; 5.5 mg/kg (IQR 5.0-9.3); p < 0.001). The chance to develop antibodies to infliximab was relatively lower in OP than YP (0.329 (95% CI - 1.2 to - 1.01); p < 0.001), while the overall duration of response to IFX was not significantly different (after 2 years 53% (n = 29) in YP vs. 58% (n = 45) in OP; p = 0.56).Conclusion: Intensification of the induction scheme is suggested for PIBD patients aged < 10 years. What is Known? •Infliximab trough levels of paediatric IBD patients are influenced by several factors as dosing scheme, antibodies and inflammatory markers. •In 4.5-30% of the paediatric IBD patients, infliximab treatment was stopped within the first year. What is New? •The majority of young PIBD (< 10 years) have inadequate IFX trough levels at the start of maintenance treatment. •Young PIBD patients (< 10 years) were in need of a more intensive treatment regimen compared with older paediatric patients during 1 year of IFX treatment. •The chance to develop antibodies to infliximab was relatively higher in young PIBD patients (< 10 years).

• Klíčová slova
• Anti-TNF, Biologics, Clinical pharmacology, Crohn’s disease, Gastroenterology, Paediatric, Ulcerative colitis,
• MeSH
• dítě MeSH
• gastrointestinální látky * terapeutické užití   MeSH
• idiopatické střevní záněty * farmakoterapie   MeSH
• infliximab * terapeutické užití   MeSH
• lidé MeSH
• předškolní dítě MeSH
• retrospektivní studie MeSH
• Check Tag
• dítě MeSH
• lidé MeSH
• mužské pohlaví MeSH
• předškolní dítě MeSH
• ženské pohlaví MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• gastrointestinální látky * MeSH
• infliximab * MeSH