Methimazole Gel Pen for Cats – Pros and Cons

Feline hyperthyroidism

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The Methimazole Gel Pen can be used to treat feline hyperthyroidism.The medication is called: Methimazole: Twist-a-Dose Transdermal Gel. I guess you regulate the amount deposited (applied) by twisting the pen. The device that delivers the dose is somewhat like a felt-tip pen and it is delivered onto the hyperthyroid cat’s ear.

Hyperthyroidism raises the metabolism, makes the cat very hungry with weight loss. There are other symptoms.

The medication is methimazole (trade name: Tapazole or Felimazole) and it blocks production (synthesis) of the thyroid hormones, triiodothyronine (T3) and thyroxine (T4). The medication is absorbed into the bloodstream through the thin skin of the ear flap where there is little hair.

The upside is convenience and a reduced exposure to the medication by the pet owner. The downsides are some possible serious side effects, which should be carefully checked and explained by the vet and the possibility of a cat or dog in a multi-companion animal household licking the chemical off the cat’s ear and ingesting it. If a young kitten licks off the chemical I can imagine possible serious consequences.

As a result, steps would have to be taken in a multi-cat household to prevent that happening. What to suggest? The difficulty is knowing how long it takes to absorb into the bloodstream. I think the vet should be asked that question. If it takes 1 hour the cat’s owner can isolate the cat receiving the treatment for one hour. That is the simple solution I would have thought.

Also there are question marks about how well the medicine is absorbed into the bloodstream. Apparently a study indicated:

Only two of six cats tested had any detectable methimazole in their bloodstream¹

Methimazole is also used in treating hyperthyroidism in people. There are other versions of this drug. One is in the form a pill and it is sold as Felimazole®. One side effect of Felimazole is vomiting. This drug certainly requires careful administration and accurate dosage management. But this is a serious and common feline disease.

“Feline hyperthyroidism is one of the most common chronic diseases we see in the middle-aged and older cat”.²


  1. Ref:
  2. Your Cat ISBN9 780312 358013 quoting
  3. Photo of cat suffering from hyperthyroidism at a veterinary clinic. Published with permission but copyright the Nottingham Vet School.


19 thoughts on “Methimazole Gel Pen for Cats – Pros and Cons”

  1. I have the anti thyroid pen for my cat and wheni went to use it no gel came out of the twist tube? What am I doing wrong? How hae to you need to press the sponge applicator onto the ear to grt the gel dose?

  2. Do any of you ever have issues with the gel pen not functioning right? I’m to give two full rotations to right and insert gel onto my cats ear. Some of my pens last 3 weeks and some will not put out enough gel on the tip. Do you have these issues? My vets secretary accuses I’m not giving the right doses or I’m missing doses. Not true at all. It doesn’t take a rocket scientist to operate these pens. Let me know if you experience any issues. Thanks.

    • on when first starting the pen. I have to click a few times to get the 1st dose then it is fine. So much easier than a glove and pushing out from syringe and then applying.


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