Azathioprine (Imuran®) for Dogs and Cats


Overview of Azathioprine for Dogs and Cats

  • Azathioprine is an immunosuppressive drug that is chemically related to some anti-cancer chemotherapy agents. Also known as Imuran®, is used to treat a number of autoimmune diseases in dogs.  It is sometimes used with caution in cats. Azathioprine is often used in combination with corticosteroids. 
  • Azathioprine is used to suppress cells involved in autoimmune diseases including those involving the skin, blood, or multiple body systems. An example of the latter is systemic lupus erythematosus (or “lupus”).
  • Azathioprine suppresses the immune system by interfering with the metabolism of immune and antibody-producing cells (lymphocytes).
  • Azathioprine is a prescription drug and can only be obtained from a veterinarian or by prescription from a veterinarian.
  • This drug is not approved for use in animals by the Food and Drug Administration but it is prescribed legally by veterinarians as an extra-label drug.
  • Brand Names and Other Names of Azathioprine

  • This drug is registered for use in humans only.
  • Human formulation: Imuran® (Glaxo Wellcome) and various generic preparations
  • Veterinary formulation: None
  • Uses of Azathioprine for Dogs and Cats

  • Azathioprine is prescribed to treat a number of autoimmune diseases in dogs, including:
  • Hemolytic anemia (destruction of red blood cells leading to anemia) in dogs
  • Thrombocytopenia (low blood platelets needed for normal blood clotting)
  • Arthritis when associated with autoimmune disease
  • Skin diseases (such as pemphigus)
  • Chronic liver inflammation (chronic, active hepatitis)
  • Immune system disorders of the stomach and intestine (inflammatory bowel diseases)
  • Certain kidney diseases (glomerulonephritis)
  • Myasthenia gravis, an autoimmune disease affecting the junction of nerves and muscles
  • Precautions and Side Effects

  • While generally safe and effective when prescribed by a veterinarian, azathioprine can cause side effects in some animals.
  • Azathioprine should not be used in animals with known hypersensitivity or allergy to the drug.
  • Because azathioprine is a potent immunosuppressive drug, extreme caution should be exercised when prescribing and administering this drug.
  • This drug can suppress the immune system severely and reduce the production of needed blood cells.
  • Cats are particularly susceptible to the suppressive effects of azathioprine on blood cells. This drug should be used very cautiously and at low doses, if at all, in cats.
  • Azathioprine may interact with other medications. Consult with your veterinarian to determine if other drugs your pet is receiving could interact with azathioprine. Such drugs include certain muscle relaxants and allopurinol.
  • Symptoms of adverse effect include lethargy, fever, reluctance to move, and loss of appetite. Any of these signs should be reported to your veterinarian.
  • It is not unusual for animals to develop transient diarrhea or loose stools with oral azathioprine treatment. Often this is a mild side effect. If diarrhea persists for more than a few days after starting treatment with azathioprine, your veterinarian should be notified.
  • If animals vomit in association with azathioprine treatment, contact your veterinarian. It may be a sign of a drug-induced effect such as pancreatitis.
  • Approximately 10 percent of dogs and all cats may be extremely sensitive to azathioprine because they lack enzymes to metabolize the active drug. Therefore, animals receiving treatment should have a blood test periodically to check for numbers of blood cells.
  • Azathioprine is related to other anticancer agents and should be always kept out of reach of children and other pets in the household.
  • How Azathioprine Is Supplied

  • Azathioprine is available in 50 mg tablets.
  • Dosing Information of Azathioprine for Dogs and Cats

  • Medication should never be administered without first consulting your veterinarian.
  • The typical dose administered to dogs is 0.5 to 1.0 mg per pound (1 to 2 mg/kg) orally every day to every other day.
  • If administered to cats, the dose should be 0.15 mg per pound (0.3 mg/kg) every other day orally.
  • It typically takes several days or weeks before azathioprine produces its full therapeutic effect once treatment is initiated.
  • Azathioprine often is administered in combination with other drugs, most often corticosteroids (cortisone-like drugs) such as prednisone.
  • The duration of administration depends on the condition being treated, response to the medication and the development of any adverse effects. Be certain to complete the prescription unless specifically directed by your veterinarian. Even if your pet feels better, the entire treatment plan should be completed to prevent relapse or prevent the development of resistance.
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    Immunosuppressive & Immunomodulator Drugs



    Immunology & Immune-mediated diseases