title: Serum infliximab concentrations in pediatric inflammatory bowel disease.
abstract: OBJECTIVE
  To study serum infliximab (s-IFX) levels in pediatric patients with inflammatory bowel disease (IBD).
  
  
  METHODS
  s-IFX trough levels were measured in a total of 133 blood samples of 37 pediatric IBD patients (Crohn's disease, 23): 48 during the induction phase (weeks 2 and 6) and 85 during maintenance treatment. Antibodies to infliximab (ATI) were determined in 93 samples (30 patients). s-IFX values were related to fecal calprotectin (FC) and serum markers of inflammation.
  
  
  RESULTS
  During induction (5 mg/kg) and maintenance therapy, the median s-IFX levels were 17.6 μg/ml (range 0-48 μg/ml) and 3.55 μg/ml (range 0-40 μg/ml), respectively. The IFX levels were similar in ulcerative colitis and Crohn's disease (e.g. during maintenance median 3.2 vs. 2.8 μg/ml, p = 0.718), thus the data are pooled. During induction, the s-IFX level was associated with the total dose of IFX, that is, young children with lower body weight had lower levels (p < 0.001 at week 2 and p < 0.05 at week 6). Shorter administration interval resulted in higher trough levels (p < 0.005). All samples with undetectable s-IFX (6.8%) levels presented ATI. High inflammation (FC >1000 µg/g) during induction was associated with lower s-IFX levels (median 4.0 μg/ml, range 0.47-25 compared to median 20 μg/ml, range 0-48 when FC <1000 µg/g, p < 0.005). There was no significant association between the ESR or values of C-reactive protein and s-IFX levels during induction.
  
  
  CONCLUSIONS
  In pediatric IBD, lower body weight and higher level of intestinal inflammation are associated to s-IFX levels during induction but relation to therapeutic response is unclear.
authors.affiliation: Children´s Hospital, Helsinki University Central Hospital, Helsinki, Finland.
authors.forename: Anssi
authors.initials: A
authors.lastname: Hämäläinen
authors.forename: Taina
authors.initials: T
authors.lastname: Sipponen
authors.forename: Kaija-Leena
authors.initials: KL
authors.lastname: Kolho
mesh_terms: D000293:Adolescent; D000367:Age Factors; D000906:Antibodies / Q000097:blood; D000911:Antibodies, Monoclonal / Q000276:immunology / Q000493:pharmacokinetics* / Q000627:therapeutic use; D015415:Biomarkers / Q000097:blood; D001799:Blood Sedimentation; D002097:C-Reactive Protein / Q000378:metabolism; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D004334:Drug Administration Schedule; D005260:Female; D005765:Gastrointestinal Agents / Q000276:immunology / Q000493:pharmacokinetics* / Q000627:therapeutic use; D006801:Humans; D015212:Inflammatory Bowel Diseases / Q000097:blood* / Q000188:drug therapy* / Q000473:pathology; D000069285:Infliximab; D039841:Leukocyte L1 Antigen Complex / Q000378:metabolism; D008297:Male
chemical_list: D000906:Antibodies; D000911:Antibodies, Monoclonal; D015415:Biomarkers; D005765:Gastrointestinal Agents; D039841:Leukocyte L1 Antigen Complex; D002097:C-Reactive Protein; D000069285:Infliximab