Leflunomide

What is leflunomide?

Leflunomide is an immunomodulating agent (a substance that modifies the immune system) used to treat certain immune-mediated conditions in cats and dogs.

It is used off label (extra label) in veterinary medicine. Many drugs are commonly prescribed for off-label use in veterinary medicine. “Off label” means the drug is being used in a way that has not been reviewed or approved by the U.S. Food and Drug Administration (FDA) or Health Canada. In these instances, follow your veterinarian’s directions and cautions carefully, as they may be significantly different from those on the label.

How do I give my pet leflunomide?

• Leflunomide comes in tablet form. Compounded liquid formulations may be prescribed.
• All forms are given orally (by mouth).
• This medication may be given with or without food. If your animal vomits or acts sick after receiving the drug on an empty stomach, try giving the next dose with food or a small treat. If vomiting continues, contact your veterinarian.
• Give this medication to your pet for the entire time prescribed by your veterinarian, even if it appears that your pet is feeling better.
• Leflunomide is considered a hazardous drug, so it is essential to avoid accidental exposure. Wear gloves when handling the medication and do not handle it if you are pregnant or nursing. 
• Avoid contact with the pet’s bodily fluids and waste for 5 days after administration. 
• If your pet vomits after receiving this drug, wear gloves while cleaning up. 
• Wear chemotherapy-resistant protective gloves when cleaning urine, feces, or vomit.

This medication should take effect within 1 to 2 days, although outward signs may not be noticeable.

What if I miss giving my pet the medication?

If you miss a dose, give it as soon as you remember, and then wait the recommended time for the next dose, as prescribed by your veterinarian. Do not give the pet two doses at once.

Are there any potential side effects?

Leflunomide may cause the following side effects:

• Lack of energy
• Loss of appetite
• Nausea

Serious adverse reactions may occur. If any of the following signs develop, stop giving leflunomide and contact your veterinarian immediately:

• An allergic reaction such as irregular breathing or difficulty breathing, rash, fever, puffiness and swelling around the face
• Seizures or convulsions
• Fever
• Jaundice (yellowing of skin, gums, or whites of eyes)
• Bleeding
• Severe behavior changes
• Pain

Drug sensitivities can develop over time with repeated exposure. Your pet may have no reaction after the first few doses but may develop a sensitivity later. It is important to watch for signs of an allergic reaction over the entire course of treatment and notify your veterinarian if you have any concerns. 

Other side effects may occur. If you notice anything unusual, contact your veterinarian immediately. This long-acting medication will last several weeks, though effects may last longer in pets with kidney or liver disease.

Are there any risk factors for this medication?

DO NOT USE leflunomide in:

• Pets that are allergic to any component of the medication
• Pets with liver disease
• Pets that are pregnant or nursing

USE WITH CAUTION in:

• Pets with kidney disease
• Pets with a weakened immune system
• Pets that are taking other immunosuppressive drugs
• Pets that are taking medications that may affect liver function

Are there any drug interactions I should be aware of?

Several medications should be USED WITH CAUTION when given with leflunomide, including:

• Activated charcoal
• Cholestyramine
• Furosemide
• Immunosuppressives (e.g., azathioprine, cyclosporine, glucocorticoids)
• Loperamide
• Rifampin
• Terbinafine
• Theophylline
• Vaccines, modified live virus
• Any medication that has the potential to cause hepatotoxicity (liver inflammation)

Be sure to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking before starting any new treatment.

Is any monitoring needed with this medication?

• Your veterinarian will assess fasted baseline blood work (including a complete blood count and liver enzymes) before starting this medication.
• Your veterinarian may schedule follow-up visits for monitoring, including repeat blood work assessments. In this case, follow your veterinarian’s directions.
• At home, monitor for any side effects such as those noted above. If any occur, stop using the medication and contact your veterinarian. 

How do I store leflunomide?

• Store at room temperature between 59°F to 86°F (15°C to 30°C), protected from light.
• Store compounded forms of this medication according to the label.
• Keep medication out of reach of children and pets.

What should I do in case of emergency?

If you suspect an overdose or an adverse reaction, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility. Be prepared to provide information about the product and your pet's weight and symptoms. Report any adverse effects to the FDA or Health Canada.