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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

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

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

Frequency

SID to every 48 hours

Max dose

20 mg

Duration: Limited data; use with caution

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 — 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

Educational reference only

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.

Educational reference only

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.

Educational reference only