Azathioprine
Also known as: Imuran, Azasan
**Important Information for Pet Owners:** * **Patience is Key:** This medication takes time to work. It may take **several weeks** before you see an improvement in your pet's condition. Do not stop giving the medication without consulting your veterinarian. * **Safety & Handling:** Azathioprine is a potent drug that can affect human DNA. **Wash your hands thoroughly** after handling the tablets. If you are pregnant, trying to become pregnant, or nursing, **do not handle this medication** or wear protective gloves if you must. * **Watch for Side Effects:** Because this drug suppresses the immune system and can affect the bone marrow, your pet is at a higher risk for infections and bleeding. * **When to Call the Vet:** Contact your veterinarian immediately if your pet shows signs of **abnormal bleeding, unexplained bruising, pale gums, fever, loss of appetite, vomiting, diarrhea, or lethargy**. * **Strict Monitoring:** Your pet will need frequent blood tests (especially in the first few months) to ensure the drug is not damaging their bone marrow or liver. Keep all scheduled recheck appointments.
Dosage must be set by your veterinarian for your specific pet. Never give human medication or another pet’s prescription without veterinary guidance.
What it is used for
- Inflammatory bowel disease
- Immune-mediated anemia, colitis, immune-mediated skin disease, and acquired myasthenia gravis
- Adjunctive therapy in myasthenia gravis in non-responsive patients
- Lymphoplasmacytic enteritis (if poor response to prednisolone)
- Severe cases of immune-mediated hemolytic anemia (IMHA)
- Acute immune-mediated hemolytic anemia (IMHA) with glucocorticoids
- Severe and refractory inflammatory bowel disease
- Adjunctive treatment of ocular fibrous histiocytomas
- Prevention of rejection of MHCmatched renal allografts (with cyclosporine)
- Perianal fistulas (anal furunculosis)
- Glomerulonephritis
- Chronic hepatitis (to reduce inflammation)
How it is given
Possible side effects
- Bone marrow suppression (leukopenia, anemia, thrombocytopenia)
- Gastrointestinal distress (vomiting, diarrhea, anorexia)
- Acute pancreatitis
- Hepatotoxicity
- Poor hair growth
- Increased susceptibility to secondary infections
- Increased risk of neoplastic illnesses with long-term use
Cautions & contraindications
- Known hypersensitivity to azathioprine
- Cats (generally contraindicated due to severe, potentially fatal myelotoxicity)
- > **Black Box Warning Equivalent:** Azathioprine is a known **mutagen and teratogen**. Pregnant women or those trying to conceive should avoid handling this medication. If handling is necessary, strict use of protective gloves is required. * **Hepatic Dysfunction:** Use with extreme caution in patients with pre-existing liver disease, as hepatotoxicity is a known adverse effect. * **Thiopurine Methyltransferase (TPMT) Deficiency:** Dogs have variable TPMT activity (similar to humans). Dogs with low TPMT activity are at a significantly higher risk for severe bone marrow suppression. * **Tapering:** In recovering patients (e.g., IMHA), withdrawal of the drug must be tapered very slowly over several months. Rapid withdrawal can trigger a rebound hyperimmune response and fatal relapse. * **Pregnancy/Nursing:** FDA Category D (human). Distributed into milk; use milk replacer if the dam is treated.
Drug interactions
- ACE Inhibitors (e.g., benazepril, enalapril): Increased potential for hematologic toxicity
- Allopurinol: Decreases hepatic metabolism of azathioprine; significantly increases toxicity risk. Dose of azathioprine must be reduced to 1/4 to 1/3 of the usual dose if used concurrently.
- Aminosalicylates (e.g., sulfasalazine, mesalamine, olsalazine): Increased risk for azathioprine toxicity
- Non-depolarizing muscle relaxants (e.g., pancuronium, tubocurarine): Neuromuscular blocking activity may be inhibited or reversed by azathioprine
- Corticosteroids: Often used together intentionally, but carries a greater potential risk for overall toxicity development
- Drugs affecting myelopoiesis (e.g., trimethoprim/sulfa, cyclophosphamide): Increased potential for hematologic toxicity (additive bone marrow suppression)
- Warfarin: Potential for reduced anticoagulant effect
- Aminosalicylates: Increased risk of azathioprine toxicity.
- ACE inhibitors: May increase the potential for haematological adverse events (e.g., severe anaemia or leucopenia).
Frequently asked questions
What is Azathioprine used for in pets?
**Important Information for Pet Owners:** * **Patience is Key:** This medication takes time to work. It may take **several weeks** before you see an improvement in your pet's condition. Do not stop giving the medication without consulting your veterinarian. * **Safety & Handling:** Azathioprine is a potent drug that can affect human DNA. **Wash your hands thoroughly** after handling the tablets. If you are pregnant, trying to become pregnant, or nursing, **do not handle this medication** or wear protective gloves if you must. * **Watch for Side Effects:** Because this drug suppresses the immune system and can affect the bone marrow, your pet is at a higher risk for infections and bleeding. * **When to Call the Vet:** Contact your veterinarian immediately if your pet shows signs of **abnormal bleeding, unexplained bruising, pale gums, fever, loss of appetite, vomiting, diarrhea, or lethargy**. * **Strict Monitoring:** Your pet will need frequent blood tests (especially in the first few months) to ensure the drug is not damaging their bone marrow or liver. Keep all scheduled recheck appointments.
Is Azathioprine safe for my pet?
Dosage must be set by your veterinarian for your specific pet. Never give human medication or another pet’s prescription without veterinary guidance.
This article is for general education and is not a substitute for professional veterinary advice. If your pet is unwell, please consult a veterinarian.
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