|Systematic (IUPAC) name|
|Trade names||Azasan, Imuran and others|
|Licence data||US FDA:|
|Pregnancy cat.||D (AU) D (US)|
|Legal status||℞ Prescription only|
|Routes||Mainly oral (sometimes initially intravenous)|
|Metabolism||Activated non-enzymatically, deactivated mainly by xanthine oxidase|
|Half-life||26–80 minutes (azathioprine)
3–5 hours (drug plus metabolites)
|Excretion||Renal, 98% as metabolites|
55774-33-9 (sodium salt)
|Mol. mass||277.263 g/mol|
|Melt. point||238–245 °C (460–473 °F)|
| (what is this?)
Azathioprine (INN, pron.: //, abbreviated AZA) is an immunosuppressive drug used in organ transplantation and autoimmune diseases and belongs to the chemical class of purine analogues. Synthesized originally as a cancer drug and a pro-drug for mercaptopurine in 1957, it has been widely used as an immunosuppressant for more than 50 years.
Azathioprine acts as a pro-drug for mercaptopurine, inhibiting an enzyme that is required for the synthesis of DNA. Thus it most strongly affects proliferating cells, such as the T cells and B cells of the immune system.
The main adverse effect of azathioprine is bone marrow suppression, which can be life-threatening, especially in people with a genetic deficiency of the enzyme thiopurine S-methyltransferase. It is also listed by the International Agency for Research on Cancer as a Group 1 carcinogen (carcinogenic to humans).
Azathioprine is produced by a number of manufacturers under different brand names (Azasan by Salix in the U.S., Imuran by GlaxoSmithKline in Canada, the U.S., Australia, Ireland and Great Britain, Azamun in Finland and Imurel in Scandinavia and France, among others).
Medical uses 
Azathioprine is used alone or in combination with other immunosuppressive therapy to prevent rejection following organ transplantation, and to treat an array of autoimmune diseases, including rheumatoid arthritis, pemphigus, systemic lupus erythematosus, Behçet's disease and other forms of vasculitis, autoimmune hepatitis, atopic dermatitis, myasthenia gravis, neuromyelitis optica (Devic's disease), restrictive lung disease, and others. It is also an important therapy and steroid-sparing agent for inflammatory bowel disease (such as Crohn's disease and ulcerative colitis) and for multiple sclerosis, which are immune-mediated as well.
Kidney or Liver transplantation 
Azathioprine is used to prevent rejections of kidney or liver allografts, usually in conjunction with other therapies including corticosteroids, other immunosuppressants, and local radiation therapy. The administration protocol starts either at the time of transplantation or within the following two days.
Rheumatoid arthritis 
Being a disease-modifying antirheumatic drug (DMARD), azathioprine has been used for the management of the signs and symptoms of adult rheumatoid arthritis. Nonsteroidal anti-inflammatory drugs (NSAIDs) and corticosteroids may be combined or continued (if they were already in use) with azathioprine, but the combination with other DMARDs is not recommended.
Crohn's disease 
Azathioprine has been used in the management of moderately to severely or chronically active Crohn's disease, to maintain clinical remission (absence of disease activity) in corticosteroid-dependent patients, and to provide benefit in patients with fistulizing Crohn's disease. The onset of action is slow and it may require several months to achieve clinical response.
Lower doses of azathioprine are used as a therapy in children with refractory or corticosteroid-dependent Crohn's disease, without causing many side effects; however the long-term risks may still outweigh benefits.
It was shown to be very effective in eczema and atopic dermatitis in researches, even though it is not commonly used. The British National Eczema Society lists it as a third-line treatment for severe to moderate cases of these skin diseases.
It was widely used for the treatment of multiple sclerosis until the first half of the 1990s. Concerns about increased risk of malignancy has led to a decreased use, yet it is still used in maintenance treatment for patients who frequently relapse.
Adverse effects 
Nausea and vomiting are common adverse effects, especially at the beginning of a treatment. Such cases are met with taking azathioprine after meals or transient intravenous administration. Side effects that are probably hypersensitivity reactions include dizziness, diarrhea, fatigue, and skin rashes. Hair loss is often seen in transplant patients receiving the drug, but rarely occurs under other indications. Because azathioprine suppresses the bone marrow, patients can develop anaemia and will be more susceptible to infection; regular monitoring of the blood count is recommended during treatment. Acute pancreatitis can also occur, especially in patients with Crohn's disease.
The enzyme thiopurine S-methyltransferase (TPMT) is responsible for various activation and deactivation steps in azathioprine's mechanism of action, and genetic polymorphisms of TPMT leads to decreased methylation and decreased inactivation of 6MP. This can result in dangerous bone marrow suppression, and an assay of TPMT in red blood cells or a TPMT gene test can avoid this complication. TMPT polymorphisms occur with a frequency of about 5%, meaning that 0.3% of patients have defects on both of their TMPT genes; they are homozygous.
Azathioprine is listed as a human carcinogen in the 12th Report on Carcinogens by the National Toxicology Program of U.S. Department of Health and Human Services, asserting that it is "known to be a human carcinogen based on sufficient evidence of carcinogenicity from studies in humans." Since August 2009, the U.S. Food and Drug Administration has required warnings to be placed on packaging with respect to increased risks of certain cancers.
The risks involved seem to be related both to the duration and to the dosage used. People who have previously been treated with an alkylating agent may have an excessive risk of cancers if treated with azathioprine. Epidemiological studies by International Agency for Research on Cancer (IARC) have provided "sufficient" evidence of azathioprine carcinogenicity in humans (Group 1), although the methodology of past studies and the possible underlying mechanisms are questioned.
The various diseases requiring transplantation may in themselves increase the risks of non-Hodgkin's lymphoma, squamous cell carcinomas of the skin, hepatobiliary carcinomas, and mesenchymal tumours to which azathioprine may add additional risks. Those receiving azathioprine for rheumatoid arthritis may have a lower risk than those undergoing transplantation.
Cases of hepatosplenic T-cell lymphoma – a rare type of lymphoma – have been reported in patients treated with azathioprine. The majority occurred in patients with inflammatory bowel disease. Adolescents and young adult males were the majority of cases. They presented with a very aggressive disease course and, with one exception, died of the lymphoma. The FDA has required changes to the labeling to inform users and clinicians of the issue.
Skin cancers 
In transplant patients, skin cancer is 50 to 250 times more common than in the general population, and between 60% and 90% of patients are affected 20 years after transplantation. The use of immunosuppressive medication including azathioprine in organ transplantation has been linked to increased rates of developing skin cancer. Azathioprine causes the accumulation of 6-thioguanine (6-TG) in patients' DNA, which might trigger cancer when the patient is later exposed to ultraviolet light. Patients taking azathioprine were found to be abnormally sensitive to UVA light.
Drug interactions 
Other purine analogues such as allopurinol inhibit xanthine oxidase, the enzyme that breaks down azathioprine, thus increasing the toxicity of azathioprine. On the other hand, low doses of allopurinol have been shown to safely enhance the efficacy of azathioprine, especially in inflammatory bowel disease non-responders. This may still lead to lower lymphocyte counts and higher rates of infection, therefore the combination requires careful monitoring.
Azathioprine decreases the effects of the anticoagulant warfarin and of non-depolarizing muscle relaxants, but increases the effect of depolarizing muscle relaxants. It can also interfere with niacin (vitamin B3), resulting in at least one case to pellagra and fatal medullary aplasia. It has also been reported to cause vitamin B12 deficiency.
Large single doses are generally well tolerated; a patient who took 7.5 g azathioprine (150 tablets) at once showed no relevant symptoms apart from vomiting, slightly decreased white blood cell count and marginal changes in liver function parameters. Main symptoms of long-term overdosing are infections of unclear origin, mouth ulcers and spontaneous bleeding, all of which are consequences of the bone marrow suppression.
Pregnancy and breastfeeding 
Azathioprine can cause birth defects. A 2003 population-based study in Denmark showed that the use of azathioprine and related mercaptopurine resulted in a seven-fold incidence of fetal abnormalities as well as a 20-fold increase in miscarriage. Birth defects in a child whose father was taking azathioprine have also been reported. Although no adequate and well-controlled studies have taken place in humans, when given to animals in doses equivalent to human dosages, teratogenesis was observed. Transplant patients already on this drug should not discontinue on becoming pregnant. This contrasts with the later-developed drugs tacrolimus and mycophenolate, which are contraindicated during pregnancy.
Traditionally, as for all cytotoxic drugs, the manufacturer advises not to breastfeed whilst taking azathioprine. However, the "Lactation Risk Category" reported by Thomas Hale in his book "Medications and Mothers' Milk" lists azathioprine as "L3", termed "moderately safe".
Azathioprine is absorbed from the gut to about 88%. Bioavailability varies greatly between individual patients, between 30 and 90%, because the drug is partly inactivated in the liver. Highest blood plasma concentrations, counting not only the drug itself but also its metabolites, are reached after one to two hours; and the average plasma half-life is 26 to 80 minutes for azathioprine and three to five hours for drug plus metabolites. 20 to 30% are bound to plasma proteins while circulating in the bloodstream.
Azathioprine is a prodrug, a substance that is not an active drug itself but is activated in the body. This happens in several steps; at first it is slowly and almost completely converted to 6-mercaptopurine (6-MP) by reductive cleavage of the thioether (–S–). This is mediated by glutathione and similar compounds in the intestinal wall, the liver and on red blood cells, without the aid of enzymes. 6-MP is metabolized analogously to natural purines, giving thioguanosine triphosphate (TGTP) and thio-deoxyguanosine triphosphate (TdGTP) via thioinosine monophosphate (TIMP) and several further intermediates. On a second path, the sulfur atom of 6-MP and TIMP is methylated. The end products of azathioprine metabolism are thiouric acid (38%) and various methylated and hydroxylated purines, which are excreted via the urine.
Mechanism of action 
The purine molecule is the framework for two of the four bases that occur in DNA, adenine and guanine. Consequently, blocking the synthesis of purine also hinders DNA synthesis and thus inhibits the proliferation of cells, especially fast-growing cells without a method of nucleotide salvage ("recycling"), such as lymphocytes. Two types of lymphocytes, T cells and B cells, are particularly affected by the inhibition of purine synthesis.
Azathioprine's active metabolite methyl-thioinosine monophosphate (MeTIMP) is a purine synthesis inhibitor that works by blocking the enzyme amidophosphoribosyltransferase, possibly among others. Additional mechanisms, mediated by other metabolites, have been discovered several decades after the drug's introduction, mainly in the 1990s and 2000s: Thioguanosine triphosphate (TGTP) is incorporated into RNA, compromising its functionality. It also interacts with the GTP-binding protein Rac1, blocking upregulation of the protein Bcl-xL and thus sending activated T cells into apoptosis (a kind of programmed cell death). The closely related thio-deoxyguanosine triphosphate (TdGTP) is built into DNA. Thioinosinic acid impedes later steps of DNA synthesis via enzymes such as adenylosuccinate synthase and IMP dehydrogenase. Moreover, azathioprine blocks the downstream effects of CD28 costimulation, a process required for T cell activation.[verification needed] In vivo data indicate inflammatory bowel disease patients treated with azathioprine have more mononuclear cells that have undergone apoptosis than untreated controls, indicating this mechanism may be responsible for the in vivo response to the drug in this disease.
Physical and chemical properties 
Azathioprine is a thiopurine linked to a second heterocycle (an imidazole derivative) via a thioether. It is a pale yellow solid with a slightly bitter taste and a melting point of 238–245 °C. It is practically insoluble in water and only slightly soluble in lipophilic solvents such as chloroform, ethanol and diethylether. It dissolves in alkaline aqueous solutions, where it hydrolyzes to 6-mercaptopurine.
Azathioprine is synthesized from 5-chloro-1-methyl-4-nitro-1H-imidazole and 6-mercaptopurine in dimethyl sulfoxide (DMSO). The synthesis of the former starts with an amide from methylamine and diethyl oxalate, which is then cyclizised and chlorinated with phosphorus pentachloride; the nitro group is introduced with nitric and sulfuric acid.
Azathioprine was synthesized by George Herbert Hitchings and Gertrude Elion in 1957 (named BW 57-322) to produce 6-mercaptopurine (6-MP) in a metabolically active but masked form, and at first used as a chemotherapy drug.
Robert Schwartz investigated the effect of 6-MP on the immune response in 1958 and discovered that it profoundly suppresses the formation of antibodies when given to rabbits together with antigens. Following the work done by Sir Peter Medawar and Gertrude Elion in discovering the immunological basis of rejection of transplanted tissues and organs, and Schwartz's researches on 6-MP, Sir Roy Calne, the British pioneer in transplantation, introduced 6-MP as an experimental immunosuppressant for kidney and heart transplants. When Calne asked Elion for related compounds to investigate, she suggested azathioprine, which was subsequently found out to be superior (as effective and less toxic to the bone marrow) by Calne. On 5 April 1962, with regimens consisting of azathioprine and prednisone, the transplantation of kidneys to unrelated recipients (allotransplantation) was successful for the first time. For many years, this kind of dual therapy with azathioprine and glucocorticoids was the standard antirejection regimen, until ciclosporin was introduced into clinical practice (by Calne as well) in 1978.
Ciclosporin has now replaced some of the azathioprine use due to a longer survival time, especially in heart-related transplantations. Moreover, despite being considerably more expensive, mycophenolate mofetil is also increasingly being used in place of azathioprine in organ transplantation, as it is associated with less bone marrow suppression, fewer opportunistic infections, and a lower incidence of acute rejection.
- American Society of Health-System Pharmacists (January 2012). "Azathioprine, Azathioprine Sodium". AHFS Drug Information 2012. American Society of Health-System Pharmacists. ISBN 978-1-58528-267-8.
- Elion, G. (1989). "The purine path to chemotherapy". Science 244 (4900): 41–47. doi:10.1126/science.2649979. PMID 2649979.
- Maltzman, J. S.; Koretzky, G. A. (2003). "Azathioprine: Old drug, new actions". Journal of Clinical Investigation 111 (8): 1122–1124. doi:10.1172/JCI18384. PMC 152947. PMID 12697731.
- Patel, A. A.; Swerlick, R. A.; McCall, C. O. (2006). "Azathioprine in dermatology: The past, the present, and the future". Journal of the American Academy of Dermatology 55 (3): 369–389. doi:10.1016/j.jaad.2005.07.059. PMID 16908341.
- Evans WE. (2004). "Pharmacogenetics of thiopurine S-methyltransferase and thiopurine therapy.". Ther Drug Monit. 26 (2): 186–91. PMID 15228163.
- International Agency for Research on Cancer (IARC) (1987). "Azathioprine". Summaries & Evaluations (World Health Organization). suppl. 7: 119.
- Nuyttens, J. J.; Harper, J.; Jenrette, J. M.; Turrisi, A. T. (2005). "Outcome of radiation therapy for renal transplant rejection refractory to chemical immunosuppression". Radiotherapy and Oncology 74 (1): 17–19. doi:10.1016/j.radonc.2004.08.011. PMID 15683663.
- Remuzzi, G.; Lesti, M.; Gotti, E.; Ganeva, M.; Dimitrov, B.; Ene-Iordache, B.; Gherardi, G.; Donati, D. et al. (August 2004). "Mycophenolate mofetil versus azathioprine for prevention of acute rejection in renal transplantation (MYSS): a randomised trial". The Lancet 364 (9433): 503–12. doi:10.1016/S0140-6736(04)16808-6. PMID 15302193.
- Suarez-Almazor, M. E.; Spooner, C.; Belseck, E. (2000). "Azathioprine for treating rheumatoid arthritis". In Suarez-Almazor, Maria E. Cochrane Database of Systematic Reviews. doi:10.1002/14651858.CD001461.
- Sandborn, W. J. (1998). "Azathioprine: State of the art in inflammatory bowel disease". Scandinavian journal of gastroenterology. Supplement 225: 92–99. PMID 9515759.
- Biancone, L.; Tosti, C.; Fina, D.; Fantini, M.; De Nigris, F.; Geremia, A.; Pallone, F. (2003). "Maintenance treatment of Crohn's disease". Alimentary Pharmacology and Therapeutics 17: 31–37. doi:10.1046/j.1365-2036.17.s2.20.x. PMID 12786610.
- Rutgeerts, P. (2004). "Treatment of perianal fistulizing Crohn's disease". Alimentary Pharmacology and Therapeutics 20: 106–110. doi:10.1111/j.1365-2036.2004.02060.x. PMID 15352905.
- Kirschner, B. S. (1998). "Safety of azathioprine and 6-mercaptopurine in pediatric patients with inflammatory bowel disease". Gastroenterology 115 (4): 813–821. doi:10.1016/S0016-5085(98)70251-3. PMID 9753482.
- McGovern, D. P. B.; Jewell, D. P. (2005). "Risks and benefits of azathioprine therapy". Gut 54 (8): 1055–1059. doi:10.1136/gut.2004.053231. PMC 1774869. PMID 16009676.
- Abu-Shakra, M.; Shoenfeld, Y. (2001). "Azathioprine therapy for patients with systemic lupus erythematosus". Lupus 10 (3): 152–153. doi:10.1191/096120301676669495. PMID 11315344.
- Olszewska, M.; Kolacinska-Strasz, Z.; Sulej, J.; Labecka, H.; Cwikla, J.; Natorska, U.; Blaszczyk, M. (2007). "Efficacy and safety of cyclophosphamide, azathioprine, and cyclosporine (ciclosporin) as adjuvant drugs in pemphigus vulgaris". American journal of clinical dermatology 8 (2): 85–92. PMID 17428113.
- Richman, D. P.; Agius, M. A. (2003). "Treatment of autoimmune myasthenia gravis". Neurology 61 (12): 1652–1661. PMID 14694025.
- Meggitt, S. J.; Gray, J. C.; Reynolds, N. J. (2006). "Azathioprine dosed by thiopurine methyltransferase activity for moderate-to-severe atopic eczema: A double-blind, randomised controlled trial". The Lancet 367 (9513): 839–846. doi:10.1016/S0140-6736(06)68340-2. PMID 16530578.
- Casetta, I.; Iuliano, G.; Filippini, G. (2009). "Azathioprine for multiple sclerosis". Journal of Neurology, Neurosurgery & Psychiatry 80 (2): 131–132; discussion 132. doi:10.1136/jnnp.2008.144972. PMID 19151017.
- Jasek, W, ed. (2007). Austria-Codex (in German) (62nd ed.). Vienna: Österreichischer Apothekerverlag. pp. 4103–9. ISBN 978-3-85200-181-4.
- Weersma, R. K., Peters, F. T. M., Oostenbrug, L. E., van den Berg, A. P., van Haastert, M., Ploeg, R. J., Posthumus, M. D., Homan van der Heide, J. J., Jansen, P. L. M. and van Dullemen, H. M. (October 2004). "Increased incidence of azathioprine-induced pancreatitis in Crohn's disease compared with other diseases". Alimentary Pharmacology & Therapeutics 20 (8): 843–850. doi:10.1111/j.1365-2036.2004.02197.x. PMID 15479355.
- Fujita K, Sasaki Y (August 2007). "Pharmacogenomics in drug-metabolizing enzymes catalyzing anticancer drugs for personalized cancer chemotherapy". Curr. Drug Metab. 8 (6): 554–62. doi:10.2174/138920007781368890. PMID 17691917.
- Yates, C. R.; Krynetski, E. Y.; Loennechen, T.; Fessing, M. Y.; Tai, H. L.; Pui, C. H.; Relling, M. V.; Evans, W. E. (1997). "Molecular diagnosis of thiopurine S-methyltransferase deficiency: Genetic basis for azathioprine and mercaptopurine intolerance". Annals of internal medicine 126 (8): 608–614. PMID 9103127.
- Payne, K.; Newman, W.; Fargher, E.; Tricker, K.; Bruce, I. N.; Ollier, W. E. R. (2007). "TPMT testing in rheumatology: Any better than routine monitoring?". Rheumatology 46 (5): 727–729. doi:10.1093/rheumatology/kel427. PMID 17255139.
- Mutschler, Ernst; Schäfer-Korting, Monika (2001). Arzneimittelwirkungen (in German) (8 ed.). Stuttgart: Wissenschaftliche Verlagsgesellschaft. pp. 107, 936. ISBN 3-8047-1763-2.
- Carol Eustice (October 23, 2005). "Blood Donation - Are rheumatoid arthritis patients able to donate blood?". About.com. Retrieved November 29, 2011.
- National Toxicology Program (10 June 2011). "Report On Carcinogens – Twelfth Edition – 2011" (PDF). National Toxicology Program. Retrieved June 20, 2012.
- "FDA: Cancer Warnings Required for TNF Blockers". FDA. August 4, 2009. Retrieved June 20, 2012.
- International Agency for Research on Cancer (IARC) (1981). "Azathioprine – 5. Summary of Data Reported and Evaluation". Summaries & Evaluations (World Health Organization) 26: 47.
- Gombar V, Enslein K, Blake B, Einstein K (1993). "Carcinogenicity of azathioprine: an S-AR investigation". Mutat Res 302 (1): 7–12. doi:10.1016/0165-7992(93)90083-8. PMID 7683109.
- "Imuran (azathioprine) Tablets and Injection". FDA. May 2011. Retrieved June 20, 2012.
- "Skin cancer alert for organ drug". BBC Online. BBC news. September 15, 2005. Retrieved June 10, 2012.
- O'Donovan, P.; Perrett, C. M.; Zhang, X.; Montaner, B.; Xu, Y. Z.; Harwood, C. A.; McGregor, J. M.; Walker, S. L. et al. (2005). "Azathioprine and UVA Light Generate Mutagenic Oxidative DNA Damage". Science 309 (5742): 1871–1874. doi:10.1126/science.1114233. PMC 2426755. PMID 16166520.
- Sahasranaman, S.; Howard, D.; Roy, S. (2008). "Clinical pharmacology and pharmacogenetics of thiopurines". European Journal of Clinical Pharmacology 64 (8): 753–767. doi:10.1007/s00228-008-0478-6. PMID 18506437.
- Chocair P, Duley J, Simmonds HA, et al. (1993). "Low-dose allopurinol plus azathioprine/cyclosporin/prednisolone, a novel immunosuppressive regimen.". Lancet 342: 83–84. PMID 8100914.
- Sparrow MP, Hande SA, Friedman S, et al. (2005). "Allopurinol safely and effectively optimizes tioguanine metabolites in inflammatory bowel disease patients not responding to azathioprine and mercaptopurine". Aliment Pharmacol Ther 22: 441–6. PMID 16128682.
- Sparrow, M. P.; Hande, S. A.; Friedman, S.; Cao, D.; Hanauer, S. B. (2007). "Effect of Allopurinol on Clinical Outcomes in Inflammatory Bowel Disease Nonresponders to Azathioprine or 6-Mercaptopurine". Clinical Gastroenterology and Hepatology 5 (2): 209–214. doi:10.1016/j.cgh.2006.11.020. PMID 17296529.
- Govani SM, Higgins PD (2010). "Combination of thiopurines and allopurinol: adverse events and clinical benefit in IBD". J Crohns Colitis 4: 444–9. PMID 21122542.
- Ansari AR, Patel N, Sanderson J, et al. (2010). "Low dose azathioprine or 6-mercaptopurine in combination with allopurinol can bypass many adverse drug reactions in patients with inflammatory bowel disease.". Aliment Pharmacol Ther 31 (6): 640–647. PMID 20015102.
- Oliveria A, Sanches M, Selores M (2011). "Azathioprine-induced pellagra". J Dermatol 38: 1035–7. PMID 21658113.
- Kim CJ, Park K, Inoue H, et al. (1998). "Azathioprine-lnduced megaloblastic anemia with pancytopenia 22 years after living-related renal transplantation". Int J Urol 5: 100–102. PMID 9535611.
- Dinesh K. Mehta (March 2003). British National Formulary, Issue 45. Pharmaceutical Society of Great Britain. London: British Medical Association. ISBN 0-85369-555-5.
- Cleary, B. J.; Källén, B. (2009). "Early pregnancy azathioprine use and pregnancy outcomes". Birth Defects Research Part A: Clinical and Molecular Teratology 85 (7): 647–654. doi:10.1002/bdra.20583. PMID 19343728.
- Tagatz, G. E.; Simmons, R. L. (1975). "Pregnancy after renal transplantation". Annals of internal medicine 82 (1): 113–114. PMID 799904.
- Nørgård, B.; L. Pedersen, K. Fonager, S. Rasmussen, H. Sørensen (March 2003). "Azathioprine, mercaptopurine and birth outcome: a population-based cohort study". Alimentary pharmacology and therapeutics 17 (6): 827–834. doi:10.1046/j.1365-2036.2003.01537.x. PMID 12641505.
- Tallent, M. B.; Simmons, R. L.; Najarian, J. S. (1970). "Birth defects in child of male recipient of kidney transplant". JAMA: the journal of the American Medical Association 211 (11): 1854–1855. PMID 4905893.
- Polifka, J. E.; Friedman, J. M. (2002). "Teratogen update: Azathioprine and 6-mercaptopurine". Teratology 65 (5): 240–261. doi:10.1002/tera.10043. PMID 11967923.
- Thomas W. Hale (April 2010). Medications and Mothers' Milk: A Manual of Lactational Pharmacology. Hale Pub. ISBN 978-0-9823379-9-8.
- Cronstein, B. N. (2004). "Pharmacogenetics in the rheumatic diseases". Annals of the Rheumatic Diseases 63 (Suppl 2): ii25–ii27. doi:10.1136/ard.2004.028217. PMC 1766779. PMID 15479867.
- Karran, P.; Attard, N. (2008). "Thiopurines in current medical practice: Molecular mechanisms and contributions to therapy-related cancer". Nature Reviews Cancer 8 (1): 24–36. doi:10.1038/nrc2292. PMID 18097462.
- Dinnendahl, V, Fricke, U, ed. (2011). Arzneistoff-Profile (in German) 2 (25 ed.). Eschborn, Germany: Govi Pharmazeutischer Verlag. ISBN 978-3-7741-9846-3.
- Steinhilber, D; Schubert-Zsilavecz, M; Roth, HJ (2005). Medizinische Chemie (in German). Stuttgart: Deutscher Apotheker Verlag. p. 340. ISBN 3-7692-3483-9.
- "Azathioprine Pathway". Small Molecule Pathway Database. Retrieved 31 August 2012.
- Cara, C. J.; Pena, A. S.; Sans, M.; Rodrigo, L.; Guerrero-Esteo, M.; Hinojosa, J.; García-Paredes, J.; Guijarro, L. G. (2004). "Reviewing the mechanism of action of thiopurine drugs: Towards a new paradigm in clinical practice". Medical science monitor : international medical journal of experimental and clinical research 10 (11): RA247–RA254. PMID 15507865.
- US Patent 3056785, G. H. Hitchings; Yonkers & G. B. Elion, "Purine Derivatives", issued 1962-10-06 .
- Blicke, F. F.; Godt, H. C. (1954). "Diuretics. I. 3-Substituted Paraxanthines". Journal of the American Chemical Society 76 (14): 3653. doi:10.1021/ja01643a015.
- Elion, G. B.; Callahan, S. W.; Hitchings, G. H.; Rundles, R. W. (1960). "The metabolism of 2-amino-6-(1-methyl-4-nitro-5-imidazolyl)thiopurine (B.W. 57-323) in man". Cancer chemotherapy reports. Part 1 8: 47–52. PMID 13849699.
- Thiersch, J. B. (1962). "Effect of 6-(1'-methyl-4'-nitro-5'-imidazolyl)-mercaptopurine and 2-amino-6-(1'-methyl-4'-nitro-5'-imidazolyl)-mercaptopurine on the rat litter in utero". Journal of reproduction and fertility 4: 297–302. PMID 13980986.
- Schwartz, R.; Stack, J.; Dameshek, W. (1958). "Effect of 6-mercaptopurine on antibody production". Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine 99 (1): 164–167. PMID 13601801.
- Calne, R. Y. (1960). "The rejection of renal homografts". The Lancet 275 (7121): 417–418. doi:10.1016/S0140-6736(60)90343-3.
- Murray, J. E.; Merrill, J. P.; Harrison, J. H.; Wilson, R. E.; Dammin, G. J. (1963). "Prolonged Survival of Human-Kidney Homografts by Immunosuppressive Drug Therapy". New England Journal of Medicine 268 (24): 1315–1323. doi:10.1056/NEJM196306132682401. PMID 13936775.
- Bakker, R. C.; Hollander, A. A. M. J.; Mallat, M. J. K.; Bruijn, J. A.; Paul, L. C.; De Fijter, J. W. (2003). "Conversion from cyclosporine to azathioprine at three months reduces the incidence of chronic allograft nephropathy". Kidney International 64 (3): 1027–1034. doi:10.1046/j.1523-1755.2003.00175.x. PMID 12911553.
- Henry, M. L.; Sommer, B. G.; Ferguson, R. M. (1985). "Beneficial effects of cyclosporine compared with azathioprine in cadaveric renal transplantation". The American Journal of Surgery 150 (5): 533. doi:10.1016/0002-9610(85)90431-3.
- Modry, D. L.; Oyer, P. E.; Jamieson, S. W.; Stinson, E. B.; Baldwin, J. C.; Reitz, B. A.; Dawkins, K. D.; McGregor, C. G. et al. (1985). "Cyclosporine in heart and heart-lung transplantation". Canadian journal of surgery. Journal canadien de chirurgie 28 (3): 274–280, 282. PMID 3922606.
- Woodroffe R, Yao G, Meads C, Bayliss S, Ready A, Raftery J, Taylor R (2005). "Clinical and cost-effectiveness of newer immunosuppressive regimens in renal transplantation: a systematic review and modelling study". Health Technol Assess 9 (21): 1–194. PMID 15899149.
- Imuran (GlaxoSmithKline Patient Information Leaflet)
- Azasan (manufacturer's website)
- U.S. National Library of Medicine: Drug Information Portal - Azathioprine