• Renal and other solid-organ transplant rejection prophylaxis
• Severe rheumatoid arthritis (DMARD)
• Systemic lupus erythematosus with major organ involvement
• Crohn's disease and ulcerative colitis (steroid-sparing maintenance)
• Autoimmune hepatitis maintenance
• Myasthenia gravis (specialist use)
• Pemphigus and severe atopic dermatitis (refractory cases)

Azathioprine is non-enzymatically converted to 6-mercaptopurine, then metabolised by HGPRT to thioinosine monophosphate and ultimately to 6-thioguanine nucleotides, which are incorporated into DNA. This produces strand breakage and inhibits T-cell and B-cell proliferation. The drug also inhibits Rac1 GTPase in activated T cells, promoting apoptosis.

• Adults: 1–3 mg/kg/day orally, adjusted by clinical response and serum 6-thioguanine levels.
• TPMT genotype/phenotype testing recommended before initiation to identify poor metabolisers at risk of severe myelosuppression.
• Monitor CBC and LFTs weekly initially, then monthly.

• Bone marrow suppression (leucopenia most common), nausea, vomiting, hepatotoxicity, increased infection risk, hypersensitivity reactions, pancreatitis.
• Long-term: increased risk of skin cancers and lymphoma.
• Rare: hepatosplenic T-cell lymphoma (with IBD).

• Hypersensitivity to azathioprine or 6-mercaptopurine.
• TPMT deficiency.
• Severe bone marrow suppression.
• Pregnancy (Category D).
• Concomitant allopurinol or febuxostat without significant dose reduction (xanthine oxidase inhibition raises toxicity).
• Active serious infection.

Store below 30 °C in a dry place, protected from light and moisture.