Abstract
BACKGROUND: Azathioprine (AZA) and its close analog 6-mercaptopurine are thiopurines widely used in the treatment of patients with cancer, organ transplantation, and autoimmune or inflammatory diseases, including systemic lupus erythematosus. Bone marrow inhibition is a common side effect of AZA, and severe bone marrow inhibition is related to decreased thiopurine S-methyltransferase (TPMT) activity. CASE SUMMARY: We herein report a patient with proliferative lupus nephritis who was using AZA for maintenance therapy, had no common TPMT pathogenic site mutations, and exhibited severe bone marrow inhibition on the 15(th) day after oral administration. CONCLUSION: This report alerts physicians to the fact that even though the TPMT gene has no common pathogenic site mutation, severe myelosuppression may also occur.