Therapeutic Drug Monitoring of Golimumab to Predict Disease Activity and Antidrug Antibodies Status in Patients with Ankylosing Spondylitis

BACKGROUND AND AIM: Golimumab is a fully human tumor necrosis factor-alpha inhibitor that is highly effective in the management of ankylosing spondylitis (AS). A major limitation of golimumab is nonresponse, resulting from low drug concentrations, which is primarily due to antidrug antibodies (ADAs). The aim of this study was to assess the trough concentration of golimumab and the prevalence of ADA formation in patients with AS. METHODS: An enzyme-linked immunosorbent assay was used to quantify golimumab trough concentrations and ADAs in 59 Iraqi patients with AS; AS disease activity was also evaluated using the Ankylosing Spondylitis Disease Activity Score (ASDAS). Regression analysis was performed to determine predictors of disease activity and ADA formation. RESULTS: The mean age of the participants was 37.86 years, most of them (52 patients) were men, and the median number of golimumab doses administered was 7. The median ASDAS score was 3.1, and approximately 35% of patients had low disease activity (ASDAS score <2.1). The range of golimumab trough concentration was 0.21-1.38 mg/L with a median of 0.41 mg/L, and ADAs were detected in 8 patients (13.6%). Trough concentrations were higher in ADA-negative patients and were significantly negatively correlated with ASDAS scores. Regression analysis identified the trough drug concentration as the only predictor of both disease activity and ADA formation, with lower concentrations responsible for higher disease activity and a higher chance of developing ADAs. CONCLUSIONS: Drug concentration is an important determinant of disease activity, and routine monitoring of trough concentration is recommended for therapeutic drug monitoring of golimumab.