Major Uses

Azathioprine is an immunosuppressive drug. In dogs, it is used to treat immune-related illnesses such as Lupus, Rheumatoid arthritis, autoimmune skin diseases, and some types of kidney disease. In cats, it is used to treat Inflammatory Bowel Disease, commonly coupled with the corticosteroids Prednisone or Prednisolone.

Common Precautions

This medication also suppresses bone marrow, the body's blood cell producer, so anemic animals should be very closely monitored while using Azathioprine and given a reduced dose. Although suppressing the immune system is the desired effect, animals and humans with suppressed immune systems are much more prone to infection and disease, thus health-conscious, preventative measures should be taken to protect the animal's overall wellbeing while using this medication.

Since Azathioprine can suppress human immune systems as well, protective gloves should be worn while handling the medication.

Cats are highly sensitive to bone marrow medications, so many veterinarians advise against using Azathioprine for treating feline autoimmune disorders. Close monitoring and care should be given if prescribed to a cat.

Treatment should not suddenly be stopped, as the animal's immune system could overreact and cause the disorder or disease to flare up again. Beneficial effects may take up to six weeks to become apparent, so it is important to give the animal plenty of time before assuming the medication is not working.

Azathioprine should not be administered in animals with a known allergy or hypersensitivity to the drug. It is advised to contact a veterinarian if diarrhea or vomiting occur.


Azathioprine should be kept in a closed container at room temperature and away from sunlight. If kept in these conditions, it will remain stable for 60 days. If administering intravenously, the injectable solution (Azathioprine powder mixed with water) should be used within 24 hours.


Offered in both oral and injectable forms, Azathioprine is available in 25, 50, 75, and 100mg tablets along with a 10mg/mL solution for injection.

If treating a small dog, 2mg/kg should be administered every 24 hours by mouth initially then 0.5-1mg/kg every 48 hours. Doses may vary in different species, when the drug is given by a different route or concurrently with other medications, and with regards to a patient's age, breed, and health status. A veterinarian's dosing instructions and/or those printed on the medication label should be followed closely.

Success of this medication is heavily based on consistency and stability, so skipping doses is detrimental to the animal's health. If a dose is missed, it should be given as soon as it is remembered; however, if it is within a few hours of the next regularly scheduled dose, skip the missed dose completely.

This information is for general reference only and should not be used for the diagnosis or treatment of any condition of your pet. It's intended as a general reference, this information may not include all possible uses, precautions, directions, reactions (including allergic), drug interactions, or withdrawal times. Always consult your local veterinarian and have your pet examined for any advice concerning the diagnosis and treatment of your pet, including which products and doses are most appropriate. Any trademarks are the property of their respective owners. VetDepot is not a pharmacy. All prescription products are dispensed by our Pharmacy Partner. Article last updated 2/2014.