Initiating azathioprine for Crohn's disease.

Azathioprine (AZA) and 6-mercaptopurine are therapeutic options for patients with moderate to severe inflammatory Crohn's disease. AZA has both a complex metabolism and potential for adverse events that can be clinically challenging. AZA has been shown to maintain remission and reduce corticosteroid use in patients with Crohn's disease. There is heterogeneous thiopurine methyltransferase metabolism among patients, which has implications for clinical dosing and risk for adverse events. Routine thiopurine methyltransferase testing before the initiation of AZA will reduce early leukopenia and is mandatory to avoid potentially life-threatening myelotoxicity. Thiopurine metabolite assays may aid in the assessment of adherence and adverse events. Patients who do not respond to AZA therapy may benefit from the addition of biologic therapy or methotrexate.