Rapid Quantification of Infliximab in Plasma and Serum Using MabTrack ELISA

The therapeutic chimeric antibody infliximab affects tumour necrosis factor alpha (TNF) and is frequently administered to patients who suffer from rheumatic arthritis, intestinal disorders, dermatological diseases and cancer. TNF plays an important role in inflammation; it causes for example pain, swollen joints and stiffness in rheumatoid arthritis patients. Inhibition of TNF is therefore believed to relieve some of these symptoms and thus to improve quality of life of patients.

Plasma and serum levels of TNF inhibitors are highly variable between patients, and clearly correlate to the clinical symptoms in patients. In approximately 8%-43% of the patients treated with infliximab, antibodies are formed directed towards infliximab. This can partially hamper the function of the TNF inhibitor and can cause a reduction in plasma concentration of the TNF inhibitor. Identification of drug levels can be important for patient adjusted treatment schedules, as low drug levels are frequently an indication for antibody formation against infliximab. In addition, low drug levels may be a sign of ineffectiveness of infliximab before rebound of clinical symptoms. Alternatively, it is proposed that in patients that respond well to infliximab, the dosing of infliximab can be reduced according to serum concentrations. Drug level tests can therefore help to adapt patient medication or to switch to an alternative TNF inhibitor. This infliximab level ELISA has been developed for fast, reproducible and specific quantification of infliximab concentrations in plasma and serum.

For professional use only

The MabTrack level infliximab ELISA is a “sandwich-type” of enzyme immunoassay. In the microtiter plates, TNF is captured by monoclonal antibodies coated to polystyrene microtiter wells. The infliximab, present in the patient sample, the calibrator or the controls, binds to the TNF on the microtiter plate. Non-bound material is then removed by washing. Subsequently, a horseradish peroxidaselabeled monoclonal anti-drug antibody is added. This antibody binds to the infliximab/TNF/anti-TNF complex present in the microtiter well. After removal of non-bound HRP conjugate by washing, substrate solution is added to the wells. A coloured product is formed in proportion to the amount of infliximab present in the sample, calibrator and controls. After the reaction has been terminated by the addition of a stop solution, absorbance is measured in a microtiter plate reader. From the absorbance of samples and those of the calibrator curve, the concentration of infliximab can be determined by interpolation with the calibrator curve.

Clinical optimal ranges, e.g. therapeutic cut-off, were determined at Sanquin Diagnostic Services with the infliximab ELISA for rheumatoid arthritis to be minimally 3.0 µg/mL (Van de Bemt et al. 2013). For inflammatory bowel disease, the optimal range is 3.0–7.0 µg/mL (Vande Casteele et al.). The MabTrack level infliximab kit is calibrated on the WHO International Standard sold by the National Institute for Biological Standards and Control (#16/170).

For in vitro diagnostic use only. Reagents should be stored at 2–8°C. Leaking or damaged vials must not be used. Reagents (unopened or opened) should not be used beyond the expiration date, which is printed on the label of the vial. The reagent cannot be assumed to be free from infectious agents.

Wash hands thoroughly after handling. Wear protective gloves/protective clothing/eye protection/face protection.

Care must be taken in the use and disposal of each container and its contents. Waste-disposal, after completion of the test, should be performed according to your laboratory regulations.

Causes serious eye irritation. IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing. If eye irritation persists: get medical advice/attention. Absorb spillage to prevent material damage.

– The flat-bottom microtiter plate consists of 12 strips of 8 wells ready for use. All the wells are coated with TNF-specific mouse monoclonal antibody and recombinant TNF. The microtiter plate is vacuum sealed in a plastic pouch containing desiccant. The kit provides the flexibility to use the microtiter plate on separate occasions. Determine the number of strips required to test the desired number of samples plus 8 wells needed for running calibrators and controls. Remove strips that will not be used from the microtiter plate-frame and re-pack them in the plastic pouch containing the desiccant.
– After opening, all reagents and the microtiter plate strips may be used for ≤ 6 weeks if stored at 2–8 °C.
– Consult the enclosed information leaflet for the kit specific infliximab concentrations in calibrator 1-6 and in control 1 and control 2.

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