Ustekinumab (Stelara¬ģ) - Therapeutic Drug Monitoring (TDM)

Ustekinumab is a fully human IgG1? monoclonal antibody to interleukin (IL)-12/23 produced in a murine myeloma cell line using recombinant DNA technology, used to reduce symptoms in inflammatory conditions.

Ustekinumab binds with specificity to the shared p40 protein subunit of human cytokines interleukin (IL)-12 and IL-23. By preventing p40 from binding to the IL-12Rb1 receptor on the surface of immune cells, ustekinumab inhibit the bioactivity of human IL-12 and IL-23 protein. Abnormal regulation of IL 12 and IL 23 has been associated with immune mediated diseases, such as psoriasis, psoriatic arthritis and Crohn’s disease.

Clinical Use

In Europe, ustekinumab is indicated for the treatment of:

  • moderate to severe plaque psoriasis, in adults and children above the age of 12 years whose condition has not responded to or who cannot use other systemic (whole-body) psoriasis treatments
  • active psoriatic arthritis in adults who have not responded well enough to other disease-modifying anti-rheumatic drugs
  • moderately to severely active Crohn‚Äôs disease in adults whose condition has not responded well enough to other treatments for Crohn‚Äôs disease or who cannot receive such treatment.

Testing ustekinumab concentration:

The assay is performed using Enzyme Linked Immunosorbent Assay (ELISA). The limit of quantification (LOQ) for ustekinumab in serum is 0.005 ¬Ķg/mL.

Testing ustekinumab anti-drug antibodies (ADA):

The assay is performed using radioimmunoassay (RIA). The limit of quantification (LOQ) for ADA is 12 AU/mL.

Clinical Relevance

No response or loss of response of treatment with ustekinumab.

During treatment, some patients may develop antibodies to ustekinumab; anti-drug antibodies (ADA).

With level testing of biologics, efficacy of therapy can be improved, as treatment decisions may need to be adapted depending on the test results in conjunction with clinical responses to treatment.

Data and interpretation of ustekinumab ADA and its serum levels are still very limited.

Personalized Medicine

Monitoring biologic levels in individual patients allows optimization of treatment efficacy by adjusting therapy depending on the specific response of the patient. When drug levels are decreased in a non-responder, this may reflect formation of inactivating antibodies directed to the biologic treatment. Immunogenicity testing identifies presence or absence of inactivating antibodies, which guides the next treatment decision ‚Äď switch to other biological treatment, lowering of dose or intensify dosing. Reducing drug dosage in well-responding patients with relatively high drug levels cuts down cost. A personalized approach can improve therapy efficacy and quality of life.

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