Ustekinumab (UST) is a fully human monoclonal antibody that binds to the p40 subunit common to IL-12 and IL-23 thereby preventing the interaction with the cytokine receptors on T cells, natural killer cells and antigen-presenting cells (1). UST has been approved for treatment of moderate to severe Crohn’s disease (CD), plaque psoriasis and psoriatic arthritis (2,3,4).
A drug can only exert its pharmacological effect when adequate concentrations are achieved in the circulation. The serum concentration of biologicals just before the next administration, defined as trough concentration, has been used for therapeutic drug monitoring (TDM). Recent data have shown a positive relationship between UST serum concentration, either measured at trough or at an intermediate time point, and clinical outcomes in patients with Crohn’s disease and plaque psoriasis, respectively. TDM may therefore be very instrumental to optimize treatment.
The apDia Ustekinumab ELISA uses highly specific monoclonal antibodies developed at the University of Leuven, Belgium (KU Leuven). Anti-TNF drugs (like infliximab, adalimumab, golimumab) or anti-integrin α4β7 drugs (like vedolizumab) do not interfere with the measurement.
As an example of TDM, the use of UST concentration measurements in plaque psoriasis and CD is described.