Imuran (Azathioprine)

Azathioprine is employed in several immune‑mediated conditions to suppress excessive lymphocyte activity, thereby preventing tissue damage and improving clinical outcomes.

• Organ transplantation: helps prevent graft rejection by inhibiting immune cell proliferation, allowing long‑term graft survival.
• Rheumatoid arthritis: reduces joint inflammation, pain, and swelling, and slows disease progression in patients with moderate to severe disease.
• Inflammatory bowel disease: maintains remission, decreases flare frequency, and promotes mucosal healing in both Crohn’s disease and ulcerative colitis.
• Hematopoietic stem cell transplantation: reduces risk of graft‑versus‑host disease by dampening donor immune responses.

• Azathioprine is a pro‑drug that is converted intracellularly to 6‑mercaptopurine, which interferes with de novo purine synthesis. By inhibiting the formation of adenine and guanine nucleotides, it reduces DNA and RNA production, leading to decreased proliferation of rapidly dividing lymphocytes. This suppression of T‑ and B‑cell activity underlies its immunosuppressive effect in transplantation and autoimmune disorders. The active metabolites also incorporate into nucleic acids, further impairing cell replication.

Azathioprine may cause a range of adverse reactions, varying from mild to potentially life‑threatening.

Common Side Effects

• Nausea: mild to moderate stomach upset, often transient.
• Decreased appetite: reduced food intake leading to weight loss.
• Elevated liver enzymes: mild hepatic irritation detectable on blood tests.
• Leukopenia: reduced white blood cell count, increasing infection risk.
• Hair loss: temporary thinning or shedding of scalp hair.

Serious or Rare Side Effects

• Severe bone marrow suppression: pancytopenia requiring medical intervention.
• Hepatotoxicity: significant liver injury that may progress to failure.
• Pancreatitis: inflammation of the pancreas presenting with abdominal pain.
• Increased risk of malignancy: long‑term therapy may elevate cancer incidence.
• Severe allergic reaction: rash, fever, and organ involvement (Stevens‑Johnson syndrome).

When prescribing azathioprine, clinicians should observe several precautionary measures to minimise toxicity and monitor therapeutic response.

• Monitor blood counts: perform regular complete blood count tests to detect leukopenia early.
• Assess liver function: schedule periodic liver enzyme evaluations for hepatotoxicity.
• Adjust dose in renal impairment: reduce dosage according to renal function to avoid accumulation.
• Avoid live vaccines: immunosuppression increases risk of vaccine‑derived infection.
• Discuss pregnancy risks: counsel women of childbearing potential about potential fetal effects.
• Store at ambient temperature: keep tablets in original container, protect from moisture and heat.

Azathioprine interacts with several medicines, altering its efficacy or increasing the likelihood of adverse events.

Major Interactions (Avoid)

• Allopurinol: co‑administration can markedly increase azathioprine toxicity.
• Warfarin: azathioprine may potentiate anticoagulant effect, raising bleeding risk.
• Live vaccines: immunosuppression may lead to uncontrolled infection from vaccine strains.
• Methotrexate: concurrent use can increase bone marrow suppression.

Moderate Interactions (Monitor Closely)

• ACE inhibitors: combined use may heighten risk of renal dysfunction.
• Other immunosuppressants: additive immunosuppression can raise infection susceptibility.
• Rifampin: may reduce azathioprine plasma levels, decreasing effectiveness.
• Fluoroquinolones: may increase risk of tendon toxicity when combined.