Infliximab is a chimeric monoclonal antibody that binds to and neutralises the endogenous inflammatory cytokine tumor necrosis factor alpha (TNF-α). Infliximab is used in the treatment of autoimmune conditions, including inflammatory bowel disease (IBD), inflammatory arthritis and plaque psoriasis.

 

Indications for measuring +

  • To guide dose-adjustment to optimise drug efficacy
    • Exposure-response relationship of intravenous infliximab is well established in patients with IBD and positive associations are observed in patients with rheumatoid arthritis, ankylosing spondylitis, psoriatic arthritis and plaque psoriasis.
    • Patients at risk of increased infliximab clearance may benefit the most from TDM.
  • Diagnosis
    • Differentiating disease refractory to infliximab versus inadequate drug exposure

How to measure

Assay detail

See Canterbury Health Labs TNF Biologic Drugs assay information.

Timing of concentration sample collection

  • Blood samples should be taken at the drug trough, within 24 hours prior to the next dose.

How to interpret

DiseaseInductionMaintenance
IBD20-25 mg/L at week 2
15-20 mg/L at week 6  
7-10 mg/L at week 14
5-10 mg/L after week 14
>10 mg/L in perianal fistulising Crohn’s disease and acute severe ulcerative colitis  
Rheumatoid arthritisNo recommendation3-7 mg/L
Spondyloarthritis≥6-7 mg/L
Plaque psoriasis>2-5 mg/L
Hidradenitis suppurativaNo recommendation
Note: Evidence suggests that high concentrations do not lead to an increased risk of adverse effect

Factors affecting interpretation

Dose individualisation and adjustment

  • The presence of antibodies to infliximab (ATIs) can lead to high clearance and low concentrations of infliximab.  Some laboratories will do reflex testing of ATIs if infliximab is below a certain level (e.g. <2 mg/L).
  • Patients with active IBD activity may have a degree of protein losing enteropathy and/or bowel bleeding, which can lead to increased infliximab clearance by drug leaking into the bowel. Infliximab dose and/or dosing frequency may need to be increased to help attain adequate drug exposure.
  • Certain genetic variants can alter infliximab pharmacokinetics and treatment response. For instance, variants in the HLA-DQA105 allele are linked to increased risk of immunogenicity and loss of response. TDM can guide dosing escalations in patients carrying genetic variants.
  • Children typically exhibit higher infliximab clearance relative to body weight and require more frequent dosing optimisation.

Other dosing considerations

  • Some patients may have non-TNF-α driven disease, and therefore, may be unresponsive to infliximab despite high serum concentrations.
  • No dose adjustments are necessary for hepatic and renal impairment.
  • Physiological changes during pregnancy may alter infliximab pharmacokinetic properties. TDM may be required particularly if there is concern for suboptimal response.

Contacts for help with interpretation

Medicines Information ph: 03 364 0900

Key References

  1. Alsoud D, Moes DJAR, Wang Z, Soenen R, Layegh Z, Barclay M, Mizuno T, Minichmayr IK, Keizer RJ, Wicha SG, Wolbink G, Lambert J, Vermeire S, de Vries A, Papamichael K, Padullés-Zamora N, Dreesen E. Best Practice for Therapeutic Drug Monitoring of Infliximab: Position Statement from the International Association of Therapeutic Drug Monitoring and Clinical Toxicology. Ther Drug Monit. 2024 Jun 1;46(3):291-308.
  2. Barclay ML, Karim S, Helms ETJ, Keating PE, Hock B, Stamp LK, Schultz M. Infliximab and adalimumab concentrations and anti-drug antibodies in inflammatory bowel disease control using New Zealand assays. Intern Med J. 2019 Apr;49(4):513-518

Last updated

October 2024