Carbimazole

What is carbimazole?

Carbimazole is a medication used to treat an overactive thyroid (hyperthyroidism) in cats and other animals. Carbimazole lowers thyroid hormone levels.

It is used off label (extra label) in veterinary medicine in Canada and the United States. 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 very carefully, as they may be significantly different from those on the label.

How do I give my pet carbimazole?

• Carbimazole comes in tablet form. 
• Tablets 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.

This medication should start to take effect within a few days, although effects may not be noticeable right away. 

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 amount of time between doses. Do not give the pet two doses at once.

Are there any potential side effects from carbimazole?

Carbimazole may cause the following side effects:

• Lack of appetite and/or energy
• Vomiting

The following reactions are rare, but if they occur, contact your veterinarian immediately:

• An allergic reaction such as irregular breathing, rash, fever, puffiness and swelling around the face
• Fever, severe lack of energy, weakness/unable to get up or stand
• Severe itching or scratching, especially of the face/head

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. Other side effects may occur. If you notice anything unusual, contact your veterinarian immediately. This medication is short-acting, meaning that effects will last less than 24 hours, though effects may last longer in pets with kidney or liver disease.

Are there any risk factors for this medication?

Carbimazole should NOT BE USED in animals who:

• Are allergic to any component of the medication or are allergic to methimazole or polyethylene glycol (PEG)
• Are pregnant or nursing
• Have liver disease, diabetes mellitus, autoimmune problems, and/or blood cell problems

Carbimazole should be USED WITH CAUTION in pets who:

• Have decreased liver and/or kidney function

Are there any drug interactions I should be aware of?

Certain medications should be USED WITH CAUTION when given with carbimazole, including:

• Anticoagulants (e.g., heparin, warfarin)
• Benzimidazole antiparasitics (e.g., fenbendazole)
• Beta-blockers (e.g., atenolol, propranolol)
• Chloramphenicol
• Digoxin
• Iodine 131
• Phenobarbital
• Prednisolone/prednisone
• Theophylline

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 baseline blood work (including thyroid function), blood pressure, and body weight before starting this medication. 
• Your veterinarian will continue monitoring blood work throughout treatment.
• Your veterinarian will schedule follow-up visits for monitoring. In this case, follow your veterinarian’s directions.
• At home, monitor for any abnormal changes. If these occur, discontinue the medication and contact your veterinarian.

How do I store carbimazole?

• Store at room temperature of less than 25°C (77°F) in a tight container, protected from light.
• 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 to the medication, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility. Adverse effects should be reported to the FDA or Health Canada.