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Dear Christopher Cat

Wonder, our 12-year-old cat, was just diagnosed with hyperthyroidism, and the vet prescribed methimazole tablets to drop her thyroid function to normal.
Unfortunately, we were unable to convince Wonder to take her medicine, even when we hid the pill in a treat and used a pet piller.

Our veterinarian prescribed the same medication in a cream, which we rub onto her ears. Will this work as effectively?

Christopher Responds

For cats that don’t take pills as gracefully as I do, transdermal medications are a reasonable alternative.

Trans (through) dermal (the skin) medications are absorbed by the blood vessels under the skin, much like injectable medications. Some – but not all – medications can be formulated by a pharmacist for transdermal application.

These specially formulated medications haven’t been tested for safety or efficacy, so your veterinarian will probably start with a low dose and gradually increase it, to prevent toxicity.

Absorption through the skin varies considerably from cat to cat, especially with methimazole, so it is important to have your veterinarian do follow-up lab work to be sure Wonder isn’t absorbing too little or too much of the drug.

additional concern with transdermal medications is potential exposure of the human caregiver to the drug.

Methimazole could decrease your thyroid function, so be careful to prevent absorption through your skin, especially if you are already hypothyroid.

If the transdermal methimazole doesn’t work, consider surgery to remove the enlarged thyroid gland or radiation to shrink it.

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