What Drugs for Hyperthyroidism That Go in the Ears Are Used in Cats?

Giving Tabby transdermal methimazole is usually as easy as rubbing her ear.
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If Tabby's been diagnosed with hyperthyroidism, you've probably learned that although it's a serious condition, it's easily managed. If you've decided surgery or radioactive iodine aren't for Tabby, you have some options for medicating her. The good news is that they don't have to involve making her take a pill.


Methimazole is the medicine of choice for treating cats with hyperthyroidism. It's the generic name for Tapezole, the drug used for treating people with hyperthyroidism. It's widely available and most typically prescribed in tablet form. Some pharmacies can compound methimazole into a liquid form to be administered orally and others can incorporate it in a transdermal gel to be applied to the inside tip of Tabby's ear. Methimazole works by blocking the thyroid hormones produced by an overactive thyroid.


A second medication, carbimazole, is not a licensed drug in the US, though it is widely available for human use elsewhere in the world, including Japan, Australia and a variety of European countries. Compounding pharmacies in the US often make it available. After carbimazole is administered to a cat, it breaks down into methimazole and performs the same function of blocking thyroid hormones. Because the formulation of the drug is a bit different, the dosage for carbimazole is usually different from that of methimazole. As with methimazole, a compounding pharmacy can put it in a transdermal gel for easy application.

How Transdermal Gel Works

Much like nicotine patches that help people stop smoking, transdermal gels deliver medication by slow absorption through the skin. The hairless inside tip of a cat's ear is the ideal place to apply a gel, because it doesn't have the barrier of fur to block the medicine's absorption and it's difficult for Tabby to lick it off. The gels are designed with her skin in mind for efficient absorption and delivery of the medicine into her bloodstream.

Applying the Gel

The gel will be provided in syringes, with the dose determined by your vet. When you medicate Tabby, you should wear disposable latex gloves or finger cots. The procedure, which is very simple, involves dispensing the dose onto your gloved finger and applying it by gently rubbing it inside her ear tip. You should alternate ears so the drug's absorbed properly and to prevent it from building up on her skin over time.

Potential Side Effects

If Tabby's ears are particularly sensitive, they may become irritated from the transdermal gel, which is why it's important not to apply the medicine to the same ear over and over. The witch hazel will also gently clean away any excess medication that hasn't been absorbed. Otherwise, the potential side effects are the same as for the oral medicine: lethargy, vomiting and loss of appetite. Facial itching is rare, but more serious. If Tabby experiences any of these side effects, contact your vet so you can adjust the dosage.

Always check with your veterinarian before changing your pet’s diet, medication, or physical activity routines. This information is not a substitute for a vet’s opinion.

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