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Azathioprine

Prescription

Immunosuppressant (purine analog)

Last reviewed 21 Apr 2026 · PetCare.AI Editorial Team

Species

Dog

Brands

4 available

Interactions

6 documented

Formulations

Mechanism of action

Prodrug metabolized to 6-mercaptopurine and further to thioguanine nucleotides, which are incorporated into DNA causing chain termination; inhibits purine synthesis and T-cell proliferation, suppressing cell-mediated immunity

At a glance

Class

Immunosuppressant (purine analog)

Schedule

Prescription

Storage

Below 25°C, protect from light and moisture; handle with gloves (cytotoxic)

Dosing

🐕

Dog

Immune-mediated hemolytic anemia, inflammatory bowel disease, pemphigus, lupus

Dose

1–2.5 mg/kg

Route

Frequency

SID (initially), then every other day for maintenance

Max dose

100 mg

Duration: Weeks to months; taper slowly

Educational reference only

This information is provided for educational purposes and is not a substitute for professional veterinary advice, diagnosis, or treatment. Always consult a qualified veterinarian before administering any medication to your pet. Find a vet near you →

Formulations

💊

Tablet — 1

Strength

50mg

Available in India

Storage

Below 25°C, protect from light and moisture; handle with gloves (cytotoxic)

Safety

Absolute contraindications — do not use

USE IN CATS — EXTREME CAUTION, generally avoided
Cats are extremely sensitive to myelosuppression; if used, dose 0.3mg/kg every 48–72 hours only
Pregnancy
Teratogenic

Use with caution

Hepatic disease
Allopurinol inhibits xanthine oxidase, markedly increasing azathioprine toxicity — reduce dose by 50–75%

Adverse effects

Common

Bone marrow suppression

GI upset

Hepatotoxicity

Serious

Severe leukopenia/pancytopenia

Acute pancreatitis

Fatal myelosuppression in cats

Monitoring parameters

CBC weekly for first month, then biweeklyHepatic enzymesAmylase/lipaseSigns of infection

Educational reference only

Interactions

Major — 6

Allopurinol

major

Allopurinol inhibits xanthine oxidase which metabolizes azathioprine's active metabolite 6-MP. Concurrent use causes severe 6-MP accumulation and life-threatening myelosuppression.

Management: Reduce azathioprine dose by 25-33% when combined with allopurinol. Monitor CBC every 1-2 weeks. Some references recommend avoiding combination entirely.

Mycophenolate Mofetil

major

Both inhibit purine synthesis in lymphocytes via different mechanisms. Combined: severe additive myelosuppression.

Management: Do not combine. Choose one immunosuppressant. Monitor CBC closely during transitions.

Sulfa-Trimethoprim (TMP-Sulfa)

major

Both cause myelosuppression via folate pathway interference. Combined: severe bone marrow suppression risk.

Management: Avoid. Use amoxicillin or cephalosporin instead of TMP-sulfa during azathioprine therapy.

Chlorambucil

major

Both myelosuppressive: chlorambucil (alkylating) + azathioprine (purine analog). Severe additive bone marrow suppression.

Management: Do not combine unless under oncologist supervision with frequent CBC monitoring.

Leflunomide

major

Both are immunosuppressive via different pyrimidine/purine pathways. Combined: severe additive myelosuppression and hepatotoxicity.

Management: Do not combine. Choose one. Monitor CBC and liver enzymes during transition.

Hydroxyurea

major

Both cause myelosuppression via different mechanisms. Combined: severe additive bone marrow suppression.

Management: Avoid. If switching, monitor CBC closely during transition.

Educational reference only

Brands

International

Imuran

GlaxoSmithKline

Azasan

Salix

India

Imuran

GSK India

Azaprine

RPG Life Sciences

FAQs

Frequently asked questions

›What is Azathioprine?

Azathioprine is a immunosuppressant (purine analog) used in pets. Prodrug metabolized to 6-mercaptopurine and further to thioguanine nucleotides, which are incorporated into DNA causing chain termination; inhibits purine synthesis and T-cell proliferation, suppressing cell-mediated immunity

›What is Azathioprine used for in pets?

Azathioprine is used in veterinary medicine for: Immune-mediated hemolytic anemia, inflammatory bowel disease, pemphigus, lupus.

›What is the Azathioprine dose for dogs?

For dogs, Azathioprine is typically dosed as follows — Immune-mediated hemolytic anemia, inflammatory bowel disease, pemphigus, lupus: 1–2.5 mg/kg PO SID (initially), then every other day for maintenance. Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.

›What are the side effects of Azathioprine?

Common: Bone marrow suppression, GI upset, Hepatotoxicity. Serious (call your vet immediately): Severe leukopenia/pancytopenia, Acute pancreatitis, Fatal myelosuppression in cats.

›Does Azathioprine need a prescription?

Yes. Azathioprine is a prescription medication and should only be administered under veterinary supervision.

›When should Azathioprine not be used?

Do not use Azathioprine if: USE IN CATS — EXTREME CAUTION, generally avoided; Pregnancy.

Educational reference only