Azathioprine is a prescription drug used to treat certain autoimmune diseases in dogs. A healthy immune system destroys perceived threats like bacteria, viruses, and other harmful things. Autoimmune diseases (or immune-mediated disorders) cause the immune system to become overactive and inappropriately attack the body’s cells and tissues. Treatment for autoimmune diseases generally involves the use of drugs such as azathioprine to suppress the overactive immune system.
What does azathioprine do?
Azathioprine is an immunosuppressant drug, also known under the brand name Imuran. It suppresses cells that produce antibodies and minimizes the body’s immune response. This makes azathioprine an effective treatment for autoimmune diseases.
Azathioprine prevents the formation of purines, chemical compounds that are required to make DNA and RNA in cells. DNA is an essential part of cell replication and division in the body. Without them, cells cannot multiply. Azathioprine is particularly good at disrupting the rapid cell division that occurs in the immune system. Basically, it inhibits the body’s ability to quickly produce the cells that fight perceived threats to the body. This is why it works well to suppress an overactive immune system. However, it can also leave the immune system vulnerable to valid threats like germs.
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Your veterinarian may prescribe azathioprine along with corticosteroids such as prednisolone (which also helps suppress the immune system). In many cases, the goal of adding azathioprine to the treatment regimen is to reduce the steroid dose as much as possible. This is because the potential complications of using steroids are often worse than those of using azathioprine.
Azathioprine therapy is usually started as a once-daily dose and reduced to administration every other day. It shouldn’t be stopped suddenly unless specifically recommended by your veterinarian. Since the drug can be absorbed through the skin, it is important to wear gloves when handling it. Pregnant and immunocompromised people should not be exposed to the drug at all.
Disorders Azathioprine Can Treat
There are several diseases for 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 contacts)
- Systemic lupus erythematosus
- Pemphigus foliaceous and other autoimmune skin diseases
- Certain types of cancer
Side effects of using azathioprine
Possible side effects of azathioprine treatment in dogs include:
- Loss of appetite
- The pale appearance of gums and other mucous membranes
- Yellowing of the gums and other mucous membranes (jaundice)
- Bruising and / or bleeding (blood in the urine, nosebleeds, blood in the stool)
- Liver toxicity
- Infections (due to suppression of the immune system)
- Bone marrow suppression
Bone marrow suppression
In a healthy dog, the bone marrow makes new blood cells. With bone marrow suppression, the body cannot produce enough new blood cells. This can lead to anemia (low red blood cells), leukopenia (low white blood cells), thrombocytopenia (low blood platelets). These blood cells have many important functions in the body. Insufficient numbers can lead to organ function problems, blood clotting problems, and a weakened immune system (making them prone to infection).
Dogs receiving azathioprine should be closely monitored, especially in the early stages of use. Your vet will often do blood tests for signs of bone marrow suppression and other complications.
Considerations Before Using Azathioprine In Dogs
Any drug can have side effects and other complications. A drug like azathioprine, which suppresses immune function, can be associated with great risks. However, if your veterinarian has prescribed azathioprine for your dog, they’ll believe the benefits outweigh the risks. The disease being treated can be more dangerous than the possible side effects.
Azathioprine should be used with caution (or not at all) in dogs with one or more of the following conditions:
- Anemia (low red blood cell count)
- Leukopenia (low white blood cell count)
- Thrombocytopenia (low blood platelet count)
- Blood clots
- Pancreatitis (chronic or acute)
- Malignant lymphoma (cancer of the lymphatic system)
- Kidney disease
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Make sure your veterinarian knows what other medications you are giving your pet as some may interact with azathioprine or increase the risk associated with other drugs.
- ACE inhibitors such as enalapril and benazepril
- Aminosalicylates such as sulfasalazine and mesalamine
- Other myelosuppressive drugs such as trimethoprim / sulfa and cyclophosphamide
- Some muscle relaxants
- Warfarin (an anticoagulant)
Never change your dog’s prescribed treatments without first talking to your veterinarian.