azatiopriin

Azathioprine, sometimes spelled azatiopriin, is an immunosuppressive medication that is a prodrug of 6-mercaptopurine (6-MP). It is used to reduce immune system activity in various conditions and is available in tablet form for oral administration.

Medical uses

Azathioprine is employed to prevent organ transplant rejection and to treat a range of autoimmune diseases. These include rheumatoid arthritis, inflammatory bowel diseases (Crohn’s disease and ulcerative colitis), systemic lupus erythematosus, and certain vasculitides. It may also be used as part of combination therapy for other inflammatory or hematologic disorders under specialist care.

Mechanism of action

Once in the body, azathioprine is converted to 6-MP, which inhibits de novo purine synthesis and can be incorporated into nucleic acids. This disruption of DNA synthesis preferentially affects rapidly dividing cells, especially lymphocytes, thereby reducing immune cell proliferation and dampening immune responses.

Administration and monitoring

Azathioprine is typically given orally, with dosing adjusted to the individual and guided by response and tolerance. TPMT (thiopurine methyltransferase) activity testing before starting treatment helps identify patients at higher risk of severe myelosuppression, enabling dose adjustments. Regular monitoring includes complete blood counts and liver function tests. Dose adjustments may be required in liver or kidney impairment, or when interactions or toxicity occur.

Adverse effects and interactions

Common adverse effects include bone marrow suppression (neutropenia, anemia), hepatotoxicity, pancreatitis, nausea, and increased infection risk. Long-term use carries a small risk of malignancies such as lymphoma. It is teratogenic and should be used with caution in pregnancy. Important drug interactions include allopurinol, which increases 6-MP levels and may necessitate a reduced azathioprine dose. Live vaccines are generally avoided during treatment.