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Azathioprine by Roxane Laboratories

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General Description:

Azathioprine is used to treat immune-mediated diseases or disorders (ex. hemolytic anemia, skin disease, thrombocytopenia, rheumatoid arthritis, inflammatory bowel disease, polyarthritis, ulcerative colitis, lupus and others). It is often used in conjunction with other drugs. As this drug will suppress your pet's natural ability to fight infection, it may be more susceptible to infections at this time.

What is this drug?
  • An immunosuppressive agent (purine antagonist antimetabolite)
  • Given by mouth (also available by injection)
Reasons for prescribing:
  • Used to treat conditions caused by an overactive immune system (ex. immune-mediated skin diseases, autoimmune hemolytic anemia, thrombocytopenia, rheumatoid arthritis, inflammatory bowel disease, polyarthritis and more)
  • Often used in combination with other drugs to suppress the immune system
  • Used to prevent organ rejection post transplantation
  • Not often prescribed to cats due to its toxicity
What dogs/cats should not take this medication?
  • Breeding or pregnant pets
  • Use with caution in pets with liver disease
  • Use with extreme caution in cats as they are more susceptible to the toxic effects, especially bone marrow suppression and bleeding disorders
  • Pets with pre-existing bone marrow suppression
  • If your pet has had an allergic reaction to azathioprine or like products

Read and follow the label carefully. Wear gloves when handling this medication and wash your hands afterwards.

Give the exact amount prescribed and only as often as directed.

Giving this medication with food may minimize GI side effects.

Dogs usually receive this medication once a day at first and then once every other day.

Cats do not often receive this drug as it affects their production of blood cells. If your veterinarian does prescribe this drug for your cat, follow the dosing instructions very carefully. Watch your cat very closely for signs of infection or bleeding.

For the first couple of months, your veterinarian will monitor your pet's blood every 1-2 weeks.

Your pet will be more susceptible to infections. Avoid situations in which your pet may be exposed to other animals.

Results may not be seen for up to 6 weeks.

Give this medication for as long as veterinarian directs. Do not skip doses or stop giving the medication without consulting your veterinarian.

If your pet is om long-term therapy, do not discontinue azathioprine abruptly, as the condition may return. Your veterinarian will advise you on a dosing schedule that will taper the drug's dose over several months.

What if a dose is missed?

If a dose is missed, give it as soon as you can. If it is time already for the next dose, skip the missed dose and go back to the normal schedule. Do not give two doses at the same time.

What to tell/ask veterinarian before giving medication?

Talk to your veterinarian about:

  • When will your pet need to be rechecked
  • What tests may need to be performed prior to and during treatment with this drug
  • What are the risks and benefits of using this drug

Tell your veterinarian about:

  • If your pet has experienced side-effects on other drugs/products
  • If your pet has experienced digestive upset now or ever
  • If your pet has experienced liver or kidney disease now or ever
  • If your pet has experienced any other medical problems or allergies now or ever
  • All medicines and supplements that you are giving your pet or plan to give your pet, including those you can get without a prescription. Your veterinarian may want to check that all of your pet's medicines can be given together.
  • If your pet is pregnant or nursing or if you plan to breed your pet
Storage and Warnings:

Store in a tight, light resistant, childproof container in a cool, dry place at room temperature away from heat and direct sunlight.

Reconstituted injection should be used within 24 hours.

Keep this and all medication out of reach of children and pets.

Wear gloves while handling this medication as it can cause side effects in humans. Pregnant women should not handle this drug.

Call your physician immediately if you accidentally take this product.

Potential side effects:
  • Most common side effect is bone marrow suppression. If you notice bruising, bleeding, lethargy, infection or if your pet has difficulty breathing, it may be due to anemia or a bleeding disorder. Notify your veterinarian if you notice any of these signs.
  • Infection: Monitor for abnormal breathing, fever, depression, lameness, diarrhea, change in urination or urine color
  • Vomiting, diarrhea, poor hair growth, rashes, pancreatitis (nausea, intestinal upset), liver damage (yellowing of gums, skin or eyes)
  • Azathioprine use may increase the risk of cancer later in your pet's life
  • If you notice any of these symptoms or anything else unusual, contact your veterinarian
Can this drug be given with other drugs?
  • Yes, but possible interactions may occur with allopurinol, modified live vaccines, pancuronium, some vitamins and supplements, succinylcholine and turbocaine
  • If your pet experiences any unusual reactions when taking multiple medications, contact your veterinarian.

Contact your veterinarian immediately if pet receives more than the prescribed amount.

What else should I know?

Notify your veterinarian if your animal's condition does not improve or worsens despite this treatment.

As with all prescribed medicines, azathioprine should only be given to the pet for which it was prescribed. It should be given only for the condition for which it was prescribed.

This is just a summary of information about azathioprine. If you have any questions or concerns about azathioprine or the condition it was prescribed for, contact your veterinarian.


Common Drug Name

Common Brand Names
A generic product is available.

Store at room temperature in a tightly closed container, protected from light.
Once the injectable is reconstituted (the powder is mixed with water), use within 24 hours if no preservative is present.

Azathioprine is an immunosuppressive medication, which is often used in combination with other drugs to suppress the immune system. It may take up to 6 weeks to see an effect.
Dogs: Azathioprine is approved to use as an immunosuppressive to treat immune mediated diseases, such as immune mediated hemolytic anemia, certain types of kidney disease, autoimmune skin diseases, lupus, and rheumatoid arthritis. 
Cats: Azathioprine may be used to treat autoimmune skin diseases.

Dose and Administration
Always follow the dosage instructions provided by your veterinarian. If you have difficulty giving the medication, contact your veterinarian
This medication may be taken with food, if necessary, to avoid side effects.
If you miss a dose, give it as soon as you remember. If it is almost time for the next dose, skip the one you missed and go back to the regular schedule. Do not give 2 doses at once.
This medication should only be given to the pet for whom it was prescribed. 

Possible Side Effects
The most common side effect is suppres­sion of the bone marrow. This may lead to anemia, with pale gums, weakness, and lethargy; bruising or bleeding tendencies; and decreased white blood cell counts, which may cause the animal to be more at risk of infections.
Monitor for signs of infection, such as abnormal breathing, fever, depression, lameness, change in urination or urine color, or diarrhea. 
Other side effects include vomiting, diarrhea, poor hair growth, skin rashes, pancreatitis, and liver injury, perhaps with jaundice (yellowing of the gums, skin, or eyes).
Contact your veterinarian immediately if you see any of the above signs in your pet.
If your pet experiences an allergic reaction to the medication, signs may include facial swelling, hives, scratching, sudden onset of diarrhea, vomiting, shock, seizures, pale gums, cold limbs, or coma. If you observe any of these signs, contact your veterinarian immediately.

Azathioprine can be absorbed through the skin, so wear gloves when giving it, and wash your hands afterwards. Pregnant owners should not handle this medication.
Because your pet’s immune system will be suppressed, your pet will be more susceptible to infections. Avoid situations in which your pet may be exposed to other animals (going outside unsupervised, breed shows, training classes, etc.). Anti­biotics may be given during treatment with azathioprine to help prevent infection. Do not use in breeding or pregnant animals.
Use with caution in animals with liver or pancreatic disease.
Use with extreme caution in cats, who are more susceptible to toxic effects, especially bone marrow suppression and bleeding.
Azathioprine may increase the risk of cancer in later life.
If on long-term therapy, do not discontinue the drug abruptly, since it may cause the disease to start again. The dose needs to be tapered off over several months as directed by your veterinarian.
Consult with your veterinarian regarding the physical examinations and laboratory testing necessary prior to, and during, treatment with azathioprine.

Drug, Food, and Test Interactions
Consult your veterinarian before using azathioprine with vitamins, supplements, modified live vaccines, and allopurinol, since interactions may occur.

Signs of Toxicity/Overdose
Bleeding, bruising, loss of appetite, and vomiting may be the most common signs of an overdose or toxicity. If you know or suspect your pet has had an overdose, or if you observe any of these signs in your pet, contact your veterinarian immediately.
Keep this and all other medications out of the reach of children and pets.

This information may not cover all possible uses, directions, side effects, precautions, allergic reactions, drug interactions, or withdrawal times. Always consult your own veterinarian for specific advice concerning the treatment of your pet.

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