Azathioprine for Dogs - Uses, Dosage and Side Effects

Josie F. Turner
By Josie F. Turner, Journalist specialized in Animal Welfare. May 9, 2022
Azathioprine for Dogs - Uses, Dosage and Side Effects

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Azathioprine is an immunosuppressive drug used to treat various immune-mediated or autoimmune diseases in dogs. It is not generally used therapeutically on its own, but is administered in combination with other immunosuppressive drugs. Given the seriousness of some potential adverse reactions associated with this drug, its administration requires periodic controls. Administration of the drug must be withdrawn whenever serious adverse effects are observed.

To learn more about azathioprine for dogs, AnimalWised explains its uses, dosage and potential side effects. It is vital you do not administer this immunosuppressive drug without being prescribed by a veterinarian. This is partly due to its contraindications which can lead to very severe adverse effects.

  1. What is azathioprine for dogs?
  2. Why is azathioprine given to dogs?
  3. Uses of azathioprine for dogs
  4. Dosage of azathioprine for dogs
  5. Side effects of azathioprine for dogs
  6. Contraindications of azathioprine in dogs

What is azathioprine for dogs?

Azathioprine is a potent immunosuppressive drug used to treat immune-mediated or autoimmune diseases. It is a synthetic analog of purine. This drug's immunosuppressive action works by inhibiting DNA synthesis of B and T lymphocytes. By carrying out this inhibition, it manages to interrupt the division of cells of the immune system and modulate the immune response.

In human beings, azathioprine is a drug which is often used for organ transplantation. This is very rare in veterinary medicine, so its uses are more common for the conditions we detail below. Azathioprine is used in various treatments. It is commonly sold under the trade names Imuran and Azasan. It is not sold over-the-counter, so it requires prescription for use. It can be given orally in tablet form or given intravenously as an injection.

Why is azathioprine given to dogs?

Azathioprine is used to treat immune-mediated or autoimmune diseases. These are diseases in which the immune system attacks or destroys the body's necessary cells by misrecognizing them as foreign attackers.

Generally, a clinical response is not seen for 4-8 weeks. For this reason, azathioprine is usually administered in addition to other immunosuppressive drugs that constitute the main aspect of treatment. Generally, this main administration is in the form of corticosteroids. The reason for doing so it to reduce the adverse effects of the main drug which are exacerbated by high doses and prolonged use, without diminishing their effectiveness of treatment.

Learn more with our article on corticosteroids for dogs.

Uses of azathioprine for dogs

As we have explained, azathioprine in dogs is used as an immunosuppressive drug in the treatment of immune-mediated or autoimmune diseases. Specifically, it is usually prescribed for the treatment of the following immune-mediated pathologies in dogs:

  • Immune-mediated hemolytic anemia
  • Immune-mediated thrombocytopenia
  • Inflammatory bowel disease IBD
  • Immune-mediated hepatitis
  • Immune-mediated meningoencephalitis
  • Rheumatoid arthritis
  • Lupus erythematosus
  • Pemphigus foliaceus
  • Myasthenia gravis

Some of these diseases are not always immune-mediated. However, azathioprine will only be used when they are. Learn more about the specific of certain immune-mediated diseases such as hemolytic anemia in dogs and canine inflammatory bowel disease.

Dosage of azathioprine for dogs

The dose of azathioprine for dogs usually varies throughout treatment. Specifically, the therapeutic protocol for azathioprine in dogs is usually as follows:

  1. An initial induction dose of 1.5-2.5 mg per kg of body weight is given every 24 hours.
  2. Once the lesions subside or the symptoms are controlled, it can be administered every other day.
  3. Over the long term, the dose can be reduced to 0.5-2 mg per kg of body weight every 72 hours.

Side effects of azathioprine for dogs

Azathioprine is an immunosuppressive drug that is frequently used for the treatment of immune-mediated diseases in dogs. As with all drugs, its use is not exempt from the appearance of adverse reactions.

The main side effects of azathioprine in dogs are the following:

  • Bone marrow aplasia (myelotoxicity): disappearance of the bone marrow tissue responsible for producing blood cells (red blood cells, white blood cells and platelets). As a consequence, anemia (decreased red blood cells), leukopenia (decreased white blood cells) or thrombocytopenia (decreased platelets) may appear.
  • Digestive signs: diarrhea, vomiting and anorexia are common gastrointestinal side effects of azathioprine.
  • Greater susceptibility to infections: its immunosuppressive effect makes the body less protected against pathogens, in turn increasing the potential incidence of secondary infections
  • Liver toxicity (hepatotoxicity): due to increased enzyme ALT (alanine aminotransferase).
  • .: with increased pancreatic amylase and lipase.
  • Skin reactions: including redness and swelling.

Given the myelotoxic and hepatotoxic potential of azathioprine, periodic hematological and biochemical controls are recommended. Tests should be performed every 2-4 weeks at the start of treatment, and every 3 months thereafter. Whenever an alteration is detected in routine controls, treatment should be withdrawn.

Contraindications of azathioprine in dogs

There are certain situations in which the administration of this immunosuppressant may be counterproductive. Specifically, the contraindications of azathioprine are when the dog has:

  • Allergies to azathioprine, mercaptopurine (a metabolite of azathioprine) or any drug excipients
  • Serious infections
  • Severe impairment of liver function
  • Severe bone marrow damage
  • Pancreatitis
  • Pregnancy (it is a teratogenic and embryotoxic compound)
  • Lactation (it is excreted with milk)
  • Vaccinations

Vaccines should not be given during treatment as the drug may interfere with the effectiveness of vaccination. In addition, it is important you inform your veterinarian about any other treatment your dog may be receiving. The purpose of this is to avoid the risks associated with certain drug interactions. Specifically, azathioprine can interact with:

  • Xanthine oxidase inhibitors (e.g. allopurinol)
  • Anticoagulants (e.g. warfarin)
  • Other immunosuppressants (e.g. cyclosporine or tacrolimus)
  • ACE inhibitors (e.g. enalapril or benazepril)
  • Aminosalicylates (sulfasalazine)

To learn more about immunity-related diseases and their controls, read our related article on what allergy medications are safe for dogs.

This article is purely informative. AnimalWised does not have the authority to prescribe any veterinary treatment or create a diagnosis. We invite you to take your pet to the veterinarian if they are suffering from any condition or pain.

If you want to read similar articles to Azathioprine for Dogs - Uses, Dosage and Side Effects, we recommend you visit our Medicine category.

  • Food and Drug Administration. (2018). IMURAN ® (azathioprine), 50-mg Scored Tablets, PRODUCT INFORMATION . Retrieved from:
  • Houston, D.M., & Taylor, J.A. (1991). Acute pancreatitis and bone marrow suppression in a dog given azathioprine. Can Vet J, 32(8), 496-497.
  • Wallisch, K., & Trepanier, L.A. (2015). Incidence, timing and risk factors of Azathioprine hepatotoxicosis in dogs. Journal of Veterinary Internal Medicine, 29(2), 513-518.
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Azathioprine for Dogs - Uses, Dosage and Side Effects