Therapeutic Drug Monitoring in Patients with Inflammatory Bowel Disease and Established Azathioprine Therapy

Background and objective Azathioprine is widely used in the treatment of corticosteroid-dependent and refractory inflammatory bowel disease (IBD). The efficacy of this treatment is based on the production of 6-thioguanine nucleotides, but extremely elevated levels may cause bone marrow suppression. Other azathioprine metabolites, 6-methylmercaptopurine ribonucleotides, are associated with hepatotoxicity. Therapeutic drug monitoring (TDM) may be of help in optimising azathioprine treatment, but data on TDM in established azathioprine therapy are lacking. We therefore measured metabolite levels in a small cohort of patients established on azathioprine therapy.