Azathioprine is produced by a number of generic manufacturers and as branded names (Azasan by Salix in the U.S., Imuran by GlaxoSmithKline in Canada and the U.S., Australia and UK, Azamun in Finland and Imurel in Scandinavia).
Mycophenolate mofetil is 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. However azathioprine certainly still has a major role.
It is listed as a human carcinogen in the 11th Report on Carcinogens of the U.S. Department of Health and Human Services, although they note that the International Agency for Research on Cancer (IARC) considered some of the animal studies to be inconclusive because of limitations in the study design and inadequate reporting. The risks involved seem to be related both to the duration and 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 have provided "sufficient" evidence of Azathioprine carcinogenicity in humans, although the methodology of past studies and the possible underlying mechanisms are questioned. The various diseases requiring transplantation, and thus azathioprine, 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 lesser risk than those following transplantation.
Azathioprine is not thought to cause fetal malformation (teratogenesis) and any risk to the offspring of treated women is small. A more recent product monograph produced by Glaxo Smith Kline and dated June 2005 does note that IMURAN can cause fetal harm when given to a pregnant woman. Their document also states that the drug should not be given during pregnancy or in patients of reproductive potential without careful weighing of benefit versus the risks and should be avoided whenever possible in pregnant women. It goes on to say that when used in pregnancy the patient should be apprised of the potential hazard to the fetus. While stating that no adequate and well-controlled studies have taken place in humans, it notes that 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 to the later developed drugs tacrolimus and myophenolate which are contra-indicated by the manufacturers during pregnancy. As for all cytotoxic drugs, the manufacturer advises not to breastfeed whilst taking azathioprine. The Lactation Risk Category (LAC) reported by Thomas Hale in "Medications and Mothers' Milk" lists azathioprine as "L3", termed "moderately safe".
Under FDA rules, this drug, like many others, excludes eligibility for blood donation.