• Therapeutic Class: Purine-antagonist Anti-metabolite
  • Common Uses: Immunosuppressants
  • Species: Dogs

Basic Information:

  • Mechanism: Azathioprine interferes with the synthesis of DNA by competing with purine. It inhibits the proliferation of cells, particularly T-lymphocytes, which are involved in the immune response. Additionally, it reduces the production of autoantibodies by affecting the growth of B-lymphocytes.
  • Absorption: The drug is absorbed from the gastrointestinal tract and metabolized into mercaptopurine. It is then excreted by the kidneys. Its efficacy and safety are influenced by the activity of the enzyme thiopurine methyltransferase (TMPT).

Applications & Administration:

  • Applications: Azathioprine is effective in treating autoimmune disorders and is often used in conjunction with corticosteroids to reduce their required dosage and side effects. The onset of action is slow, typically taking several weeks to become apparent.
  • Administration: It is recommended to administer this medication with food to mitigate potential gastrointestinal side effects.

Side Effects:

  • Common adverse effects include gastrointestinal upset (such as vomiting and diarrhea), bone marrow suppression (leading to leukopenia, thrombocytopenia, and anemia), pancreatitis, and hepatotoxicity.
  • Given its immunosuppressive action, there is an elevated risk of infections and neoplasia.


  • Regular monitoring with blood tests is crucial to assess liver function and bone marrow activity.
  • Azathioprine should be used cautiously in animals with pre-existing liver disease or compromised liver function.
  • It is contraindicated in pregnant or lactating animals due to its potential to cause birth defects and other reproductive harm.

Drug Interactions:

  • Azathioprine's effects can be potentiated when used with other immunosuppressants or drugs that are metabolized through similar pathways, such as certain ACE inhibitors or allopurinol, increasing the risk of toxicity.
  • It may also interact with anticoagulants like warfarin, requiring dose adjustments.


  • In the event of an overdose, prompt veterinary intervention is necessary. Treatment may include inducing emesis, administering activated charcoal, and supportive care to manage symptoms and prevent absorption.