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Adalimumab

Adalimumab (brand name Humira) is a human monoclonal antibody that has been approved by the FDA for treatment of rheumatoid arthritis, juvenile idiopathic arthritis, psoriatic arthritis; ankylosing spondylitis, pediatric and adult Crohn disease, ulcerative colitis, plaque psoriasis, hidradenitis suppurativa and uveitis. Adalimumab binds to tumor necrosis factor alpha (TNF) and prevents its binding to TNF alpha receptors. This blockade decreases the inflammatory response associated with autoimmune disorders. Because TNF alpha plays an important role in the immune system, treatment with adalimumab increases the risk of infections.

Adalimumab is usually self-administered by subcutaneous injection every other week at a fixed dose of 40 mg in adults.  More than 30% of patients do not respond to adalimumab therapy and approximately 50% of patients who responded initially become refractory over time. Loss of responsiveness may be due to formation of antibody to adalimumab that increases drug clearance or neutralizes drug effect. Anti-drug antibodies are also associated with adverse events such as serum sickness and hypersensitivity reactions. Testing for adalimumab concentration and presence of anti-adalimumab antibodies is helpful to adjust therapy when loss of clinical response is observed.

Trough levels are preferred to evaluate patients who are no longer responding to adalimumab. Patients with low circulating concentrations of adalimumab but no detectable antibody may respond to increased dosage. Patients who have low adalimumab concentration and detectable antibody may need to be changed to another TNF inhibitor. Patients with high trough concentrations of adalimumab, who are not responding may need to be switched to a medication with a different mechanism of action.

Specimen requirement is a red top tube of blood. Optimal therapeutic drug levels are disease specific, but trough levels above 5 ug/dL are generally considered to be adequate. Patients with trough adalimumab concentrations of less than or equal to 5.0 ug/mL, should be tested for antibody. Adalimumab levels above 35 ug/mL usually indicate that the sample was not a trough sample.

Silva-Ferreira F, Afonso J, Pinto-Lopes P, Magro F. A Systematic Review on Infliximab and Adalimumab Drug Monitoring: Levels, Clinical Outcomes and Assays. Inflamm Bowel Dis 2016;22:2289-2301

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