Real-World Adalimumab Trough Levels, Antidrug Antibody Levels, and Disease Activity in Rheumatoid Arthritis

Background: – The association between adalimumab trough levels and disease activity was evaluated in a real-world population with rheumatoid arthritis (RA). The distribution of adalimumab serum levels, proportion of patients with therapeutic exposure to adalimumab, and the presence of antidrug antibodies (ADAs) were explored to determine the utility of therapeutic drug monitoring in RA.Methods: – A cross-sectional study was conducted among 72 patients with RA who were treated with adalimumab at Maasstad Hospital between May 2022 and March 2023. The adalimumab trough levels and ADAs were measured at the steady state. Disease activity was assessed using the using the Disease Activity Score-28 based on C-reactive protein (DAS28-CRP). Univariable and multivariable regression analyses were conducted to examine the associations between adalimumab levels, disease activity, and clinical covariates, including sex, body mass index, and concomitant methotrexate use.Results: – The interindividual variability in the adalimumab trough levels was wide (range: 1.2–16 mcg/mL; median: 5.9 mcg/mL). No significant association was observed between the adalimumab trough levels and DAS28-CRP scores (P > 0.05). ADAs were present in 13.9% of the patients, and the drug levels were undetectable in 4.2%. The adalimumab trough levels were considerably higher in women than in men (P < 0.05), whereas extended dosing intervals were associated with lower adalimumab concentrations but not with higher disease activity.Conclusions: – The variability in adalimumab exposure is wide in patients with RA. However, no clear association was observed between adalimumab exposure and disease activity. These findings suggest that therapeutic drug monitoring aids in identifying patients with underexposure or overexposure to adalimumab and support individualized dose optimization, particularly in patients with low disease activity. Future prospective studies are required to evaluate the longitudinal effects of TDM-guided strategies.