Therapeutic Drug Monitoring
Adalimumab (ADM) is a fully human antibody that targets the pro-inflammatory cytokine TNF-alpha and is used to treat chronic inflammatory diseases like inflammatory bowel disease, rheumatoid arthritis, spondyloarthritis and plaque psoriasis. It has been shown that adalimumab can induce deep remission and improve the patient’s quality of life. Some patients do not respond to ADM therapy upon induction (primary non-responders), while others lose response over time (secondary non-responders).
A drug can only exert its pharmacologic effect when adequate concentrations are achieved in the circulation. The serum concentration of adalimumab just before the next injection, defined as the trough concentration, has been used for therapeutic drug monitoring (TDM). Recent data on TDM have shown that a good clinical response is associated with adequate trough concentrations in inflammatory bowel disease and rheumatoid arthritis patients. TDM may therefore be very instrumental to optimize treatment and to overcome secondary loss of response.
The apDia ADM ELISA uses a highly specific monoclonal antibody – Clone 40D8, developed at the K.U. Leuven – that only detects adalimumab (Humira?). Other anti- TNF drugs (for example infliximab and golimumab) do no interfere with the measurement.
As an example of TDM, the use of adalimumab trough concentration measurements in inflammatory bowel disease patients is described.
Inflammatory bowel disease
Induction therapy of adalimumab consists of a subcutaneous dose of 160 mg at week 0, followed by 80 mg at week 2 and 40 mg every other week from week 4 onwards. Upon good clinical response at week 12-14, treatment is continued (maintenance).
Maintenance phase: It has been shown that patients on maintenance therapy having sustained trough concentrations, are more likely to remain in remission than patients with undetectable trough concentrations. Thus, regularly checking ADM trough concentrations during maintenance therapy may be useful to evaluate the ADM treatment schedule and make adjustments when necessary.
Patients with low or undetectable drug concentrations may benefit from a dose increase or interval shortening, while the interval in patients with very high ADM concentrations can be safely prolonged.
Due to the dosing regimen, trough concentrations during induction at w2 and w4 are higher and serum samples need to be diluted more compared to the maintenance phase in which trough concentrations between 0.5-12 µg/ml are common.
Secondary loss of response is often due to the development of anti- drug antibodies, which have been observed despite of the fully human character of the drug. In case of undetectable trough concentrations, subsequent measurement of anti-drug antibodies may be helpful to determine the optimal treatment strategy.
Principle of the ADM ELISA
The apDia Adalimumab ELISA uses a highly specific monoclonal antibody – clone 40D8, developed at the KU Leuven - that only detects adalimumab (Humira®). Other anti-TNF drugs (like infliximab, golimumab) do not interfere with the measurement.
Microtiterstrips coated with TNF-alpha are incubated with calibrators, controls and diluted patient samples. During this incubation step ADM binds specifically to the TNF-alpha on the solid phase. After removal of the unbound serum proteins by a washing procedure, the antigen-antibody complex in each well is detected with specific peroxidase-conjugated monoclonal antibody (clone 40D8, developed at the KU Leuven) directed to ADM.
After removal of the unbound conjugate, the strips are incubated with a chromogenic solution containing tetramethylbenzidin and hydrogen peroxide: a blue colour develops in proportion to the amount of immunocomplex bound to the wells of the strips. The enzymatic reaction is stopped by the addition of 0.5M H2SO4 and the absorbance values at 450 nm are determined.
A standard curve is obtained by plotting the absorbance values versus the corresponding calibrator values. The concentration of ADM in patient samples is determined by interpolation from the calibration curve.