Hyperthyroid in Cats
Standard Protocol for Hyperthyroid Cats
When a cat is diagnosed as hyperthyroid, there should be a standard protocol to follow to continue the workup and treatment of this disease.
Please review the hyperthyroid handout if you have not already done so.
Once the initial diagnosis is made, the cat is put on a course of methimazole (Tapazole). This is usually done in a graduated manner, where the amount and frequency are gradually increased. By increasing the dose slowly, there is a minimum of adverse side effects. Typically, we will start with a half of 5 mg tab once a day for 4-5 days, then ½ BID. Sometimes we will increase that dose after another 4-5 days IF the pretreatment level is in double figures, or if the cat weighs more than 12 –13 pounds. Many times, however, 2.5 mg BID is enough to control the thyroid level.
Transdermal medication is available as well, and the same dosing strategy is employed.
After the cat has been on the methimazole for at least 1 week at the “maintenance” dose, it is time to recheck the blood (and urine, if possible). This is usually 3 weeks after starting the methimazole. When we recheck blood, DRAW ENOUGH BLOOD FOR A CBC AND CHEMISTRY PANEL, INCLUDING THE T4. This is to recheck the renal values most importantly and also recheck the liver enzyme values. In some cases, the hyperthyroid condition can hide renal failure. Once the methimazole reduces the T4 levels to within normal limits, the renal condition can be revealed. Checking the urine can also be helpful in evaluating the renal function. Sometimes we will also recommend a chest x-ray to evaluate the heart and lungs. Sometimes there can be heart changes associated with the hyperthyroid condition (hypertrophic cardiomyopathy), and rarely, there can be the metastasis of the thyroid tumor into the lungs.
REWEIGH THE CAT!!!!! On each visit!!!!
If the cat’s kidneys are bad, then the options of radioactive iodine or surgery are no longer options. Instead, we “use” the elevated thyroid levels to optimize renal function, by titrating the methimazole dose, balancing the hyperthyroid level against the renal function.
Once we re-evaluate the CBC and chemistry panel, then we can decide what to do next.
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