Objective: To identify (1) whether tumor necrosis factor inhibitor (TNFi) drug levels/anti-drug antibodies (ADAb) are associated with treatment response and disability in patients with psoriatic arthritis (PsA); and (2) the factors associated with TNFi drug levels.
Methods: Patients were recruited from a national multicenter prospective cohort with longitudinal serum samples and 28-joint count Disease Activity Scores (DAS28)/Health Assessment Questionnaire (HAQ) measurement over 12 months.
Results: Adalimumab (ADA) drug levels were significantly associated with ΔDAS28 (β 0.055, 95% CI 0.011-0.099; p = 0.014) and inversely with HAQ over 12 months (β -0.022, 95% CI -0.043 to -0.00063). Factors significantly associated with ADA drug levels were ADAb levels and body mass index.
Conclusion: Drug level testing in ADA-initiated PsA patients may be useful in determining treatment response/disability over 12 months.
Keywords: ANTI-DRUG ANTIBODIES; DRUG LEVELS; IMMUNOGENICITY; TREATMENT RESPONSE; TUMOR NECROSIS FACTOR-α INHIBITORS.