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Leflunomide

Prescription
Immunosuppressant (pyrimidine synthesis inhibitor)
Last reviewed 21 Apr 2026 · PetCare.AI Editorial Team
Species
Dog, Cat
Brands
3 available
Interactions
2 documented
Formulations
2

Mechanism of action

Prodrug converted to teriflunomide, which inhibits dihydroorotate dehydrogenase (DHODH), a key enzyme in de novo pyrimidine synthesis; preferentially suppresses rapidly dividing lymphocytes, reducing T- and B-cell proliferation

At a glance

Class
Immunosuppressant (pyrimidine synthesis inhibitor)
Schedule
Prescription
Storage
Below 25°C, protect from light and moisture

Dosing

🐕

Dog

Immune-mediated polyarthritis, IMHA refractory to standard therapy, histiocytic sarcoma adjunct
Dose
2–4 mg/kg
Route
PO
Frequency
SID
Max dose
200 mg
Duration: Long-term; taper based on clinical response
🐈

Cat

Immune-mediated conditions (limited data)
Dose
2–4 mg/kg
Route
PO
Frequency
SID to every 48 hours
Max dose
20 mg
Duration: Limited data; use with caution

Formulations

💊

Tablet — 2

Strength
10mg
Available in India
Strength
20mg
Available in India

Storage

Below 25°C, protect from light and moisture

Safety

Absolute contraindications — do not use

  • Pregnancy
    Teratogenic; extremely long half-life requires cholestyramine washout

Use with caution

  • Hepatic disease
    Hepatotoxic potential
  • Pre-existing myelosuppression
    Additive bone marrow suppression

Adverse effects

Common
GI upset (anorexia, vomiting, diarrhea)
Weight loss
Serious
Hepatotoxicity
Myelosuppression (thrombocytopenia)
Vasculitis

Monitoring parameters

CBC biweekly initiallyHepatic enzymes (ALT, ALP) monthlyTeriflunomide blood levels (target 20–40 mcg/mL)Body weight

Interactions

Major — 1

Azathioprine
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.

Moderate — 1

Phenobarbital
moderate
Phenobarbital induces CYP enzymes, potentially increasing leflunomide metabolism. Leflunomide is also hepatotoxic — additive liver injury risk with phenobarbital.
Management: Monitor hepatic enzymes closely. May need higher leflunomide dose.

Brands

International

Arava
Sanofi

India

Lefno
Cipla
Arava
Sanofi India

FAQs

Frequently asked questions

›What is Leflunomide?
Leflunomide is a immunosuppressant (pyrimidine synthesis inhibitor) used in pets. Prodrug converted to teriflunomide, which inhibits dihydroorotate dehydrogenase (DHODH), a key enzyme in de novo pyrimidine synthesis; preferentially suppresses rapidly dividing lymphocytes, reducing T- and B-cell proliferation
›What is Leflunomide used for in pets?
Leflunomide is used in veterinary medicine for: Immune-mediated polyarthritis, IMHA refractory to standard therapy, histiocytic sarcoma adjunct; Immune-mediated conditions (limited data).
›What is the Leflunomide dose for dogs?
For dogs, Leflunomide is typically dosed as follows — Immune-mediated polyarthritis, IMHA refractory to standard therapy, histiocytic sarcoma adjunct: 2–4 mg/kg PO SID. Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.
›What is the Leflunomide dose for cats?
For cats, Leflunomide is typically dosed as follows — Immune-mediated conditions (limited data): 2–4 mg/kg PO SID to every 48 hours. Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.
›What are the side effects of Leflunomide?
Common: GI upset (anorexia, vomiting, diarrhea), Weight loss. Serious (call your vet immediately): Hepatotoxicity, Myelosuppression (thrombocytopenia), Vasculitis.
›Does Leflunomide need a prescription?
Yes. Leflunomide is a prescription medication and should only be administered under veterinary supervision.
›When should Leflunomide not be used?
Do not use Leflunomide if: Pregnancy.

References

References

Textbooks & handbooks

  • Plumb, D.C. Plumb's Veterinary Drug Handbook. 10th ed., Wiley-Blackwell, 2023.
  • Vail, D.M., Thamm, D.H., & Liptak, J.M. (eds.). Withrow & MacEwen's Small Animal Clinical Oncology. 6th ed., Saunders/Elsevier, 2020.
  • Riviere, J.E., & Papich, M.G. (eds.). Veterinary Pharmacology and Therapeutics. 10th ed., Wiley-Blackwell, 2018.
  • National Research Council. Nutrient Requirements of Dogs and Cats. National Academies Press, Washington DC, 2006.
  • The Merck Veterinary Manual. Merck & Co., Online edition. https://www.merckvetmanual.com/

Clinical guidelines & consensus

  • Fletcher, D.J., Boller, M., Brainard, B.M., et al. "RECOVER Evidence and Knowledge Gap Analysis on Veterinary CPR." Journal of Veterinary Emergency and Critical Care, 2012;22(S1):S102–S131.
  • American Animal Hospital Association. 2018 AAHA Diabetes Management Guidelines for Dogs and Cats. AAHA Press.

Journals & peer-reviewed studies

  • Hogan, D.F., Fox, P.R., Jacob, K., et al. "Secondary prevention of cardiogenic arterial thromboembolism in the cat: The FAT CAT study." Journal of Veterinary Cardiology, 2015;17(Suppl 1):S306–S317.
  • Boswood, A., Häggström, J., Gordon, S.G., et al. "Effect of Pimobendan in Dogs with Preclinical Myxomatous Mitral Valve Disease and Cardiomegaly: The EPIC Study — A Randomized Clinical Trial." Journal of Veterinary Internal Medicine, 2016;30(6):1765–1779.
  • ASPCA Animal Poison Control Center. Toxicology and Poison Management Guidelines. American Society for the Prevention of Cruelty to Animals. https://www.aspca.org/pet-care/animal-poison-control

Regulatory & approvals

  • Central Drugs Standard Control Organisation (CDSCO), Government of India. Veterinary Drug Approval Registry, 1969–2026. Directorate General of Health Services. https://cdsco.gov.in/

Databases

  • Washington State University, College of Veterinary Medicine. Veterinary Clinical Pharmacology Laboratory (VCPL) — MDR1 Multidrug Sensitivity Database. https://vcpl.vetmed.wsu.edu/
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 →

Related medicines

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Azathioprine
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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
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Mycophenolate Mofetil
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Prodrug hydrolyzed to mycophenolic acid; selectively inhibits inosine monophosphate dehydrogenase (IMPDH), blocking de novo purine synthesis in T and B lymphocytes, which depend exclusively on this pathway for proliferation
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