What is a major safety concern when using azathioprine or 6-mercaptopurine in IBD?

• A. Renal toxicity
• B. Severe hypoglycemia
• C. Bone marrow suppression
• D. Cardiac arrhythmias

Answer: (C)

Bone marrow suppression is the major safety concern with azathioprine and 6-mercaptopurine in IBD. These thiopurines suppress immune activity by inhibiting purine synthesis, but this also reduces the bone marrow’s production of white cells, red cells, and platelets, raising the risk of infection, anemia, and bleeding. The level of suppression can be influenced by TPMT enzyme activity; patients with low TPMT activity are at higher risk for severe myelosuppression because they accumulate more active toxic metabolites. That’s why baseline CBC and liver tests, along with TPMT activity testing when available, are important, and CBC should be monitored regularly—especially during dose changes. If cytopenias occur, adjusting the dose or stopping the drug is necessary. While hepatotoxicity and pancreatitis can occur, they are less central than bone marrow suppression in terms of the major safety concern.