title: Investigating the link between disease activity and infliximab serum levels in rheumatoid arthritis patients.
abstract: OBJECTIVE
  The aim of this study was to examine the extent to which infliximab (IFX) serum levels impact disease activity in rheumatoid arthritis (RA) patients.
  
  
  METHODS
  In this cross sectional study, serum samples were taken prior to drug infusion from 60 RA patients who had been undergoing IFX therapy > 12 months as a first line of biological treatment. Patient IFX levels were tested and then associated with clinical disease activity. Three DAS28 cut-off points, <2.6, <3.2 and <5.1 were used to determine whether detectable IFX levels were any predictor of clinical disease activity. Logistic regression analysis was run to check other possible factors associated with RA clinical outcomes such as MTX concomitant use, CRP and ESR.
  
  
  RESULTS
  Sixteen (27%) out of the 60 patients tested negative; 28 (46%) presented subtherapeutic and 16 (27%) therapeutic IFX levels. Median IFX levels were higher in patients either in remission or showing low disease activity than in those with moderate and high disease activity (p=0.014). Significant association was found between IFX levels and clinical disease activity (p=0.001). Detectable levels of IFX shows better sensitivity and specificity to identify patients with DAS28<3.2 than to identify patients with DAS28<2.6 or DAS28<5.1. Conversely, the best DAS28 cut-off to identify detectable/undetectable IFX was 3.19, with AUC under ROC curve 0.804 (Sd.E 0.070), 76% specificity and 83% sensitivity (p<0.001). MTX use, CRP and ESR did not interfere with this association. Seven out of the 8 patients with anti-IFX antibodies presented DAS28>3.2 (p=0.005).
  
  
  CONCLUSIONS
  DAS28 and IFX serum levels were shown to have an inverse correlation. Undetectable IFX serum levels were associated to RA patients presenting DAS28>3.2 meaning that DAS28 <3.2 may be useful to clinicians to evaluate patient response to drug therapy.
authors: Department of Rheumatology, Gregorio Marañón University General Hospital, Madrid, Spain. lvalor.hgugm@salud.madrid.org.
authors: L
authors: L
authors: Valor
authors: Department of Rheumatology, Gregorio Marañón University General Hospital, Madrid, Spain.
authors: D
authors: D
authors: Hernández-Flórez
authors: Department of Rheumatology, Gregorio Marañón University General Hospital, Madrid, Spain.
authors: I
authors: I
authors: de la Torre
authors: Department of Rheumatology, Gregorio Marañón University General Hospital, Madrid, Spain.
authors: T
authors: T
authors: Del Río
authors: Department of Rheumatology, Gregorio Marañón University General Hospital, Madrid, Spain.
authors: J C
authors: JC
authors: Nieto
authors: Department of Rheumatology, Gregorio Marañón University General Hospital, Madrid, Spain.
authors: C
authors: C
authors: González
authors: Department of Rheumatology, Gregorio Marañón University General Hospital, Madrid, Spain.
authors: F J
authors: FJ
authors: López-Longo
authors: Department of Rheumatology, Gregorio Marañón University General Hospital, Madrid, Spain.
authors: I
authors: I
authors: Monteagudo
authors: Department of Laboratory, Marina Baixa Hospital, Villajoyosa, Alicante, Spain.
authors: F
authors: F
authors: Llinares
authors: Department of Rheumatology, Marina Baixa Hospital, Villajoyosa, Alicante, Spain.
authors: J
authors: J
authors: Rosas
authors: Department of Social Psychology and Methodology, Autonoma University, Madrid, Spain.
authors: Jesús
authors: J
authors: Garrido
authors: Department of Rheumatology, Gregorio Marañón University General Hospital, Madrid, Spain.
authors: Esperanza
authors: E
authors: Naredo
authors: Department of Rheumatology, Gregorio Marañón University General Hospital, Madrid, Spain.
authors: Luis
authors: L
authors: Carreño
mesh_terms: D000368:Aged; D000906:Antibodies / Q000097:blood; D018501:Antirheumatic Agents / Q000276:immunology / Q000493:pharmacokinetics; D019540:Area Under Curve; D001172:Arthritis, Rheumatoid / Q000097:blood / Q000188:drug therapy / Q000503:physiopathology; D001682:Biological Availability; D001799:Blood Sedimentation; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D000069285:Infliximab / Q000276:immunology / Q000493:pharmacokinetics; D008297:Male; D008727:Methotrexate / Q000627:therapeutic use; D008875:Middle Aged; D012372:ROC Curve; D012720:Severity of Illness Index; D013030:Spain; D013223:Statistics as Topic; D016896:Treatment Outcome; D014409:Tumor Necrosis Factor-alpha / Q000037:antagonists & inhibitors*
chemical_list: D000906:Antibodies; D018501:Antirheumatic Agents; D014409:Tumor Necrosis Factor-alpha; D000069285:Infliximab; D008727:Methotrexate