Formulary
Azathioprine: Indications, Dosing, Side Effects and Interactions
Azathioprine is metabolised to mercaptopurine.
MedNext Academy | 6 min read
Azathioprine: Indications, Dosing, Side Effects and Interactions
Azathioprine is metabolised to mercaptopurine.
Drug action
Azathioprine is metabolised to mercaptopurine.
Indications and dose
**Severe acute Crohn's disease,Maintenance of remission of Crohn's disease,Maintenance of remission of acute ulcerative colitis**
- **Adult** (By Mouth): 2-2.5 mg/kg daily, some patients may respond to lower doses.
**Rheumatoid arthritis that has not responded to other disease-modifying drugs,Severe systemic lupus erythematosus and other connective tissue disorders,Polymyositis in cases of corticosteroid resistance**
- **Adult** (By Mouth): Initially up to 2.5 mg/kg daily in divided doses, adjusted according to response, rarely more than 3 mg/kg daily; maintenance 1-3 mg/kg daily, consider withdrawal if no improvement within 3 months.
**Autoimmune conditions**
- **Adult** (By Mouth, Or By Intravenous Injection, Or By Intravenous Infusion): 1-3 mg/kg daily, adjusted according to response, consider withdrawal if no improvement within 3 months, oral administration preferable, if not possible then can be given by intravenous injection (intravenous solution very irritant) or
**Suppression of transplant rejection**
- **Adult** (By Mouth, Or By Intravenous Injection, Or By Intravenous Infusion): 1-2.5 mg/kg daily, adjusted according to response, oral administration preferable, if not possible then can be given by intravenous injection (intravenous solution very irritant) or
**Severe refractory eczema, normal or high TPMT activity**
- **Adult** (By Mouth): 1-3 mg/kg daily.
**Severe refractory eczema, intermediate TPMT activity**
- **Adult** (By Mouth): 0.5-1.5 mg/kg daily.
**Generalised myasthenia gravis**
- **Adult** (By Mouth, Or By Intravenous Injection, Or By Intravenous Infusion): Initially 0.5-1 mg/kg daily, then increased to 2-2.5 mg/kg daily, dose is increased over 3-4 weeks, azathioprine is usually started at the same time as the corticosteroid and allows a lower maintenance dose of the corticosteroid to be used, oral administration preferable, if not possible then can be given by intravenous injection (intravenous solution very irritant) or
**Severe ulcerative colitis, Severe Crohn's disease for azathioprine**
- **Child 2-17 years** (By mouth): Initially 2 mg/kg once daily, then increased if necessary up to 2.5 mg/kg once daily.
**Systemic lupus erythematosus, Vasculitis, Autoimmune conditions usually when corticosteroid therapy alone has proved inadequate for azathioprine**
- **Child** (By mouth): Initially 1 mg/kg daily, then adjusted according to response to 3 mg/kg daily, consider withdrawal if no improvement within 3 months; maximum 3 mg/kg per day.
**Suppression of transplant rejection for azathioprine**
- **Child** (By mouth, or by intravenous infusion): Maintenance 1-3 mg/kg daily, adjusted according to response, consult local treatment protocol for details, oral route preferred, but if oral route is not possible then can be given by intravenous infusion, the total daily dose may alternatively be given in 2 divided doses.
Cautions
Reduce dose in elderly; reduced thiopurine methyltransferase activity
Contraindications
When used for severe refractory eczema Absent thiopurine methyltransferase (TPMT) activity; very low thiopurine methyltransferase (TPMT) activity
Side effects
General side-effects: Common or very common Bone marrow depression (dose-related); increased risk of infection; leucopenia; pancreatitis; thrombocytopenia Uncommon Anaemia; hepatic disorders; hypersensitivity Rare or very rare Agranulocytosis; alopecia; bone marrow disorders; diarrhoea; gastrointestinal disorders; neoplasms; photosensitivity reaction; pneumonitis; severe cutaneous adverse reactions (SCARs) Frequency not known Nodular regenerative hyperplasia; sinusoidal obstruction syndrome Specific side-effects: Frequency not known With oral use Nausea Side-effects, further information Side-effects may require drug withdrawal. Hypersensitivity reactions Hypersensitivity reactions (including malaise, dizziness, vomiting, diarrhoea, fever, rigors, myalgia, arthralgia, rash, hypotension and renal dysfunction) call for immediate withdrawal. Neutropenia and thrombocytopenia Neutropenia is dose-dependent. Management of neutropenia and thrombocytopenia requires careful monitoring and dose adjustment. Nausea Nausea is common early in the course of treatment and usually resolves after a few weeks without an alteration in dose. Moderate nausea can be managed by using divided daily doses, taking doses after food, prescribing concurrent antiemetics or temporarily reducing the dose.
Interactions
**Severe interactions:**
- Severe myelosuppression has been reported following concomitant administration of azathioprine and ribavirin; therefore, co-administration is not advised (see sections 4.4 and 5.2).
- There are conflicting clinical reports of interactions, resulting in serious haematological abnormalities, between azathioprine and trimethoprim/sulfamethoxazole (co-trimoxazole).
- Fatal cases have been reported in patients treated concomitantly with azathioprine and allopurinol.
**Other interactions (23):**
- Food, milk and dairy products The administration of azathioprine with food may decrease systemic exposure slightly but this is unlikely to be of clinical significance (see section 4.8).
- Therefore, azathioprine may be taken with food or on an empty stomach, but patients should standardise the method of administration.
- Vaccines The immunosuppressive activity of azathioprine could result in an atypical and potentially deleterious response to live vaccines.
- It is therefore recommended that patients do not receive live vaccines until at least 3 months after the end of their treatment with azathioprine (see section 4.4).
- A diminished response to killed vaccines is likely and such a response to hepatitis B vaccine has been observed among patients treated with a combination of azathioprine and corticosteroids.
- A small clinical study has indicated that standard therapeutic doses of azathioprine do not deleteriously affect the response to polyvalent pneumococcal vaccine, as assessed on the basis of mean...
Pregnancy
Important safety information For azathioprine MHRA/CHM advice: Thiopurines and intrahepatic cholestasis of pregnancy (May 2025) Intrahepatic cholestasis of pregnancy (ICP) has been reported in a small number of patients taking azathioprine or mercaptopurine. Due to similar metabolic pathways, the risk of ICP is considered applicable to all drugs in the thiopurine class, including tioguanine. Thiopurine-induced ICP usually occurs earlier in pregnancy than non-drug-induced ICP and may not respond to ursodeoxycholic acid, however, stopping or reducing the dose of the thiopurine may improve liver-function tests. Some case reports resulted in fetal death, therefore early diagnosis and discontinuation or dose reduction of the thiopurine may minimise adverse effects in the fetus. Healthcare professionals are advised to undertake a case-by-case assessment if ICP occurs and consider the risks versus benefits of stopping or continuing thiopurine treatment. Non-fasting serum-bile acids should be measured in patients with ICP to identify pregnancies at particular risk of spontaneous preterm birth ( 40 micromol/litre) or stillbirth ( 100 micromol/litre). Patients and carers should be advised to seek immediate medical attention if signs or symptoms of ICP occur.
Breast feeding
Present in milk in low concentration. No evidence of harm in small studies-use if potential benefit outweighs risk.
Hepatic impairment
Manufacturer advises caution (impaired metabolism)-monitor liver function and complete blood count more frequently in those with severe impairment. Dose adjustments Manufacturer advises use doses at lower end of the dose range in hepatic failure; reduce dose if hepatic or haematological toxicity occur.
Renal impairment
Caution (may result in slower elimination)-monitor complete blood count more frequently in those with severe impairment. M Dose adjustments Consider reducing starting dose (limited information available). M
Medicinal forms
Capsule,Tablet,Suspension
Clinical governance
**Author:** MedNext Clinical Team. **Clinical reviewer:** Dr Shameer Deen, MBBS, MS, MRCS. **Sources:** BNF, Indian Pharmacopoeia, CIMS India. **Correction:** Report errors at support@mednext.academy.
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