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Pet Medication 101: Methimazole

Pet medication methimazole

It’s important to understand a medication’s uses and side effects before giving it to your pet. This medication info sheet is meant to give you a good understanding of what methimazole is used for, how it works, and potential side effects in cats and dogs. Always consult a veterinarian before giving your pet any medication.

1. Drug Name:


2. Common Name or Brand Name:

Tapazole, Felimazole

3. How Dispensed:

Prescription only

4. Forms:

Tablets 5mg, Tablets 10mg

Can also be made into a liquid, chewable tablet, or transdermal form by many veterinary compounding pharmacies.

5. Drug Type/Class:

Thyroid medication

6. Uses in Cats and Dogs:

Methimazole is commonly used to manage hyperthyroidism in cats.

7. How it Works:

It blocks iodine and thyroglobulin from combining and inhibits the production of thyroid hormones.

8. Side Effects and/or Signs of Overdosage:

Most unwanted side effects are seen within the first 8 weeks of treatment. The most common adverse effects include hypersensitivity reactions, anorexia, vomiting, and depression. These symptoms are usually transient. Hematologic (blood cell) changes such as eosinophilia, leukopenia, and lymphocytosis have also been seen with this medication as well as rare instances of self-inflicted skin lesions, bleeding problems, and hepatopathy (liver disease).

9. Drug Interactions:

There are no known drug interactions although correcting the hyperthyroidism can change the elimination of certain drugs (causing their dosage to need reducing). Drugs like Beta Blockers, Digoxin, and Theophylline may all require reduced dosing if used in conjunction with methimazole.

10. Cautionary Statements:

Methimazole should be avoided in patients that have hypersensitivity reactions to methimazole. It is contraindicated in pregnant cats due to the risk of inducing severe hypothyroidism to the unborn kittens. It is also contraindicated in pets with hematologic abnormalities, autoimmune disease, and liver disease.

Read more:

Changes to Expect in My Senior Cat

Kidney Failure in Cats

Inflammatory Bowel Disease (IBD) in Cats

Need to speak with a veterinarian regarding your cat’s medication or another condition?

Click here to schedule a video consult to speak to one of our vets. You can also download the FirstVet app from the Apple App Store and Google Play Stores.

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