Leflunomide

What is this medication for?

• Immune-mediated disease alternative to azathioprine/mycophenolate: IMHA/ITP (Evans), myasthenia gravis, polymyositis/polyarthritis (3–4 mg/kg response in polyarthritis series) — anecdotal/retrospective evidence tier
• Immune-mediated disease (limited use; PK favorable — complete absorption, 60 h t½)

How is it given?

Give exactly as your veterinarian prescribed — never change the dose or stop on your own unless your veterinarian has told you to.

What if I miss a dose?

• Give it as soon as you remember — unless it is almost time for the next dose (then skip the missed one; never double up).
• Call your clinic if you miss more than one dose in a row.

Side effects — what should I watch for?

Effects listed as common in this handout

• stomach/intestinal (inappetence, diarrhea) — dose-related (Most common → start low, titrate up)
• Mild low red blood cell counts, low energy/tiredness (Observed)

Worth a phone call to your veterinarian

• Human: liver damage, high blood pressure, marrow suppression (Class monitoring)

⚠️ Contact your veterinarian or an emergency clinic IMMEDIATELY if you notice

• Trouble breathing, collapse, seizures, severe vomiting or diarrhea, facial swelling, or pale gums

Before starting (or refilling), tell your veterinarian if your pet:

• has or has had: Pregnancy
• has or has had: Hepatic impairment; combine-with-care in multi-drug immunosuppression

• is pregnant, nursing, or used for breeding
• is taking any other medications, supplements, or flea/tick products, including:
  • Other immunosuppressives
  • CYP/BCRP substrates (human — rosuvastatin class)
  • Live vaccines

Storage and handling

Room temperature, light-protected tablets.

Good to know

• The immunology triangle for exam day: azathioprine (purines) vs leflunomide (pyrimidines) vs cyclosporine (calcineurin) — three different biochemical bottlenecks, one clinical goal.
• Species PK flip: humans need loading doses (2-week t½); dogs don't (day-long t½, 5-day steady state) — the reason human regimens don't transplant directly.
• Evidence honesty: compelling anecdotes, no controlled trials — its niche is the azathioprine-intolerant or refractory patient.