Canine Azathioprine

Labrador dog lying next to bottle of pills and medication, close-up

Azathioprine is a prescription medication that is used to treat autoimmune diseases in dogs. A robust immune system fights germs, viruses, and other dangerous substances that are considered as threats. Autoimmune (or immune-mediated) illnesses result in an overactive immune system that attacks the body's cells and tissues incorrectly. Medications like azathioprine are commonly used to dampen the hyperactive immune system in autoimmune illnesses.

What Does Azathioprine Do?

Azathioprine, also known by the brand name Imuran, is an immunosuppressant medication. It reduces the body's immunological response by inhibiting cells that make antibodies. As a result, azathioprine is an effective autoimmune disease therapy.

Azathioprine prevents the creation of purines, which are important for the production of DNA and RNA in cells. DNA is required for cell replication and division in the human body. Cells cannot proliferate without it. Azathioprine is particularly effective in stopping rapid cell division, such as that seen in the immune system. It essentially prevents the body from swiftly producing cells that fight off any imagined dangers. This is why it is effective in controlling an overactive immune system. It can, however, make the immune system exposed to real dangers like infections.

A combination of azathioprine and corticosteroids such as prednisolone may be prescribed by your veterinarian (which also helps suppress the immune system). Adding azathioprine to a treatment plan often has the purpose of lowering steroid dosage as much as feasible. This is because the risks associated with steroid usage are frequently greater than those connected with azathioprine use.

Azathioprine is usually started as a once-daily dosage and gradually reduced to every other day administration. It should not be abruptly stopped unless your physician advises otherwise. Because the medicine can be absorbed through the skin, gloves should be used when working with it. The medicine should not be given to pregnant women or those who are immunocompromised.

Disorders Azathioprine Can Treat

There are several diseases in which azathioprine is a potentially effective treatment.

  • Immune-mediated thrombocytopenia (ITP; autoimmune platelet destruction)
  • Immune-mediated hemolytic anemia (IMHA; autoimmune red blood cell destruction)
  • Immune-mediated polyarthritis (rheumatoid arthritis)
  • Chronic active hepatitis (a type of liver disease)
  • Inflammatory bowel disease (severe cases)
  • Myasthenia gravis (autoimmune destruction of nerve/muscle junctions)
  • Systemic lupus erythematosus
  • Pemphigus foliaceus and other autoimmune skin diseases
  • Certain types of cancer

Side Effects of Azathioprine Use

Potential side effects of azathioprine treatment in dogs include the following:

  • Loss of appetite
  • Lethargy
  • Fever
  • Pale appearance to gums and other mucous membranes
  • Yellowing of gums and other mucous membranes (jaundice)
  • Bruising and/or bleeding (blood in urine, nosebleeds, blood in stool)
  • Liver toxicity
  • Infections (due to suppression of the immune system)
  • Bone marrow suppression

Bone Marrow Suppression

Bone marrow produces new blood cells in a healthy dog. The body is unable to manufacture sufficient quantities of new blood cells when the bone marrow is suppressed. Anemia (low red blood cells), leukopenia (low white blood cells), and thrombocytopenia are all possible outcomes (low platelets). These blood cells play a variety of roles in the body. Insufficient numbers can cause organ malfunction, blood clotting disorders, and a weaker immune system (leaving them susceptible to infections).

Dogs using azathioprine will need to be regularly supervised, especially in the beginning. Your veterinarian will monitor your blood work on a regular basis for evidence of bone marrow suppression and other issues.

Considerations Before Using Azathioprine for Dogs

Side effects and other issues can occur with any drug. A medicine that reduces immunological function, such as azathioprine, might have serious side effects. If your veterinarian has recommended azathioprine for your dog, she has determined that the benefits exceed the dangers. It's possible that the sickness being treated is more harmful than the possible adverse effects.

Azathioprine should be used with caution (or not at all) in dogs with one or more of the following conditions:

  • (low red blood cell count)
  • Leukopenia (low white blood cell count)
  • Thrombocytopenia (low blood platelet count)
  • Infections
  • Blood clots
  • Pancreatitis (chronic or acute)
  • (cancer of the lymphatic system)
  • Kidney disease

Make sure your vet knows what other medications you are giving your pet, as some may interact with azathioprine or increase the risks associated with other medications.

  • ACE inhibitors like and benazepril
  • Aminosalicylates such as sulfasalazine and mesalamine
  • Other myelosuppressive drugs like trimethoprim/sulfa and cyclophosphamide
  • Some muscle relaxants
  • Warfarin (an anticoagulant drug)

Never change your dog's prescribed treatments without first speaking with your veterinarian.