Immunosuppressants, thiopurines
ATC code: L04AX01 (Azathioprine)
Brand names
Imuran, Azasan
Prodrug converted to 6-mercaptopurine and then to 6-thioguanine nucleotides — structural analogues of purine bases. They are incorporated into DNA in dividing cells, disrupting lymphocyte proliferation and suppressing cellular immunity. Metabolism via thiopurine S-methyltransferase (TPMT) — 1 in 300 patients are TPMT-homozygous deficient and 10 % heterozygous. In these patients, severe myelosuppression risk is tens of times higher — TPMT and/or NUDT15 genotyping before initiation is mandatory.
Second line
Per 2021, 2020, 2018, azathioprine is a maintenance therapy in moderate-to-severe Crohn disease and ulcerative colitis, often combined with biologics (anti-TNF). Dose 2–2.5 mg/kg/day. Effect develops over 8–16 weeks. Reduces flare frequency, corticosteroid requirements, and hospitalization rates.
Second line
Used as a steroid-sparing agent in many autoimmune diseases. In autoimmune hepatitis — first-line maintenance after glucocorticoid induction per 2019. In SLE, used as a mycophenolate mofetil alternative in mild-to-moderate nephritis. In reproductive-age SLE patients, azathioprine is the only immunosuppressant permitted during pregnancy.
Autoimmune hepatitis, SLE, vasculitides, myasthenia gravis, pemphigus.
The drug is promoted for these uses outside international guidelines. Each entry below is analyzed against AEMPS, FDA, EMA, Cochrane and major RCTs.
Not recommended
Azathioprine is an antimetabolite immunosuppressant, a purine analogue. It is prescribed to prevent organ transplant rejection and for severe autoimmune diseases (systemic lupus erythematosus, rheumatoid arthritis, Crohn's disease) when other drugs are ineffective ( 2023, 2024). In anti-aging circles, azathioprine is occasionally promoted as a means of resetting or renewing the immune system in healthy adults. In healthy adults, no clinical studies of such use exist. The drug has serious risks: myelosuppression with risk of severe neutropenia, increased risk of lymphoma and other malignancies (especially non-Hodgkin lymphoma and skin cancer), severe hepatotoxicity, and requires thiopurine methyltransferase testing before start to prevent severe toxicity in carriers of the defective variant. If azathioprine was recommended to a healthy person for the immune system, seek a second opinion immediately.
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Boxed warning
FDA boxed warning: increased risk of malignancy (lymphoma, skin cancers, hepatosplenic T-cell lymphoma in young IBD patients on long-term combination therapy with anti-TNF agents).
FDA categories were retired in 2015 (historically D). Use in pregnancy is acceptable in SLE, IBD, and post-transplant patients — the risk of untreated disease exceeds the drug risk. In autoimmune hepatitis and SLE, azathioprine is considered the preferred immunosuppressant in pregnancy.
Transfers into milk in very small amounts. Per LactMed, use is acceptable with infant monitoring.
Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.
Azathioprine is evaluated for the following indications with varying evidence strength: Inflammatory bowel disease (IBD) (evidence tier A), Autoimmune conditions (evidence tier B), Anti-aging and longevity (evidence tier F). See the full indication matrix with dosing and citations above on this page.
Common side effects of Azathioprine (≥ 1 in 100): Nausea, vomiting (especially in the first weeks), Leukopenia, thrombocytopenia, Transaminase elevation, Fatigue, Alopecia (mild). See the Safety section for uncommon and serious reactions.
FDA category D. FDA categories were retired in 2015 (historically D). Use in pregnancy is acceptable in SLE, IBD, and post-transplant patients — the risk of untreated disease exceeds the drug risk. In autoimmune hepatitis and SLE, azathioprine is considered the preferred immunosuppressant in pregnancy.
Transfers into milk in very small amounts. Per LactMed, use is acceptable with infant monitoring.
Azathioprine is contraindicated in: Hypersensitivity; Severe myelosuppression; Severe hepatic impairment; Active severe infections; Pregnancy (except SLE and transplant indications). Full list in the Safety section.
FDA boxed warning: increased risk of malignancy (lymphoma, skin cancers, hepatosplenic T-cell lymphoma in young IBD patients on long-term combination therapy with anti-TNF agents).