Transdermal Methimazole Treatment For Hyperthyroid Cats


Katie, hyperthyroid. Bless her. Photo Alan Turkus

I’ll get straight to the point. Transdermal Methimazole treatment works but ask your vet. That is the general conclusion. I had to check. There has been a useful clinical study on this. They concluded:

“Clinical improvement, as well as a significant decrease in T4, was noted in all cats.”

T4 means serum thyroxine levels. In layman’s language the treatment reduced the amount of thyroid hormone in the cat, which is the objective because hyperthyroidism is an excess of the hormone due to over-production.

This video show how to apply the drug and clean the cat’s ears because the gel builds up. Ear cleaning should be done carefully and this presenter is careful and thoughtful. The interesting aspect of this is that the drug is absorbed through the skin and where the skin is thin allowing absorption into the bloodstream is the ear flap (the bit of the ear that you see). Applying drugs this way is called “transdermal” meaning via the skin.

There are of course some negatives to this one of which is that the ears need cleaning.  The video also covers this. The gentleman presenter has a very gentle and sensible approach which is ideal.


Hyperthyroidism is most common in middle-aged and older cats caused by these environmental factors. The prevalence is 0.33%. This means a third of one percent of all cats get it; quite a high figure when you work out the numbers – about 3 million domestic cats in the USA.

Transdermal application avoids “oral daily administration” which I presume means giving pills to a cat – hurrah! Incidentally the treatments listed on the top website (Google search) for this feline condition does not refer to transdermal methimazole. They list treatment with radioactive iodine and surgical removal of the affected thyroid gland as alternatives to oral medication.

Another benefit of this method that it requires a lower dose can be used:

“a lower dose of methimazole can be used to obtain an equivalent plasma concentration and clinical effect, with reduced risk of side-effects”

A concern is whether this treatment damages the delicate skin of the ear. Apparently the study found that it did not except for one of 13 cats. To quote:

“no cutaneous reactions were noted at the site of the application of the methimazole gel during the length of the study”

The assessment is qualified by saying that they can’t be sure there won’t be some problems in the long term. Always ask your vet about treatments such as this as they should be up to date.

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Michael Broad

Hi, I'm a 71-year-old retired solicitor (attorney in the US). Before qualifying I worked in a many jobs including professional photography. I have a girlfriend, Michelle. I love nature, cats and all animals. I am concerned about their welfare.

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