OBJECTIVE: Adalimumab (ADA) trough levels correlate with clinical remission. Despite suggestions that therapeutic drug monitoring of ADA can optimize treatment in this population, it is not yet implemented in clinical practice. This study was conducted to provide more insight in ADA trough levels and antibodies to adalimumab (ATA) in an inflammatory bowel disease (IBD) population already treated with adalimumab. DESIGN: We carried out a prospective cohort study in IBD outpatients already treated with adalimumab. METHODS: Patient demographics were collected from the electronic hospital information system. Blood was drawn for determination of ADA trough levels and ATAs. Disease activity indices for Crohn's disease and ulcerative colitis and quality of life scores were obtained by a questionnaire. RESULTS: A total of 92 patients was included. ADA levels varied from < 0.1 to 20.2 mg/L. Mean ADA level was 7.7 mg/L (SD = 4.5), 4 patients developed ATAs. ADA levels ≤ 5 mg/L were demonstrated in 27 patients (29%). The ADA level was not significantly associated with remission [P = 0.391). Quality of life score correlated with ADA level (P = 0.031). CONCLUSION: Therapeutic drug monitoring in inflammatory bowel disease outpatients revealed large interindividual differences in adalimumab trough levels. These levels were subtherapeutic in nearly a third of patients. We think, despite no significant correlation was found between adalimumab trough level and disease activity, therapeutic drug monitoring has the potential to individualize treatment in inflammatory bowel disease patients using adalimumab.</p
