Therapeutic drug monitoring of adalimumab in rheumatic patients

OBJECTIVE and DESIGN Adalimumab (ADA) is effective in the treatment of rheumatoid arthritis IRA), ankylosing spondylitis (ASI and psoriatic arthritis (PsA). Despite suggestions that therapeutic drug monitoring (TDM) of ADA can optimize treatment of this population, it is not routinely implemented in clinical practice. We therefore carried out a prospective observational cohort study by measuring ADA levels in a population of patients with rheumatic diseases and related those levels to disease activity. METHODS Patient demographics were collected from the electronic hospital information system. Blood drawn before the regular outpatient visit was used for determination of ADA trough levels and antibodies against ADA (ATA). Objectified disease activity measurements were obtained at the appointment: DAS28 for RA, ASDAS for AS, and clinical assessment for SpA. RESULTS A total of 17A patients was included. ADA levels varied from less than 0.1 to 22.0 mg/L. The mean ADA level was 6.8 mg/L (standard deviation = 4.2). 5 patients (2,9%) developed ATA. The ADA level was significantly associated with remission (P = 0.002). The mean ADA level was 7.6 mg/L in patients in remission and 5.1 mg/L in patients with active disease. Use of immunosuppressants, frequency of administration, and body mass index were identified as significant covariates. CONCLUSION TDM of ADA demonstrated large interindividual differences in ADA levels. ADA trough levels were significantly associated with disease activity. TDM has the potential to individualize treatment and further research needs to show if it increases cost-effectiveness of this expensive therapy.