University of Florida
College of Veterinary Medicine
Hyperthyroid Cat Referral Guidelines
In order for us to provide you and your client with the best possible service, please read the following
Question and Answer Guidelines.
1. How can I refer a cat for radioiodine treatment if it has a totally acceptable work‐up prior to referral?
The referring veterinarian’s patient assessment should include a T4, CBC, serum chemistry screen, and a
If the cat has been started with methimazole (Tapazole) treatment, we do not find that an impediment to
immediate treatment, so long as the cat has “passed” the Tapazole trial (see below) at your practice.
The VMTH clinicians request that the referring veterinarian do a 2‐ week Tapazole treatment trial prior to
referral. This calls for a pretreatment T4, BUN, creatinine, and urine specific gravity before beginning
Tapazole treatment at the standard beginning dose of 2.5 ‐ 5.0 Bid and again after ‐2 weeks of Tapazole
treatment. What we are trying to avoid is having a cat go into renal failure after it receives the I131.
If the BUN and creatinine are elevated along with the cat having isosthenuria or hyposthenuria,
radioiodine treatment will not be done and medical treatment will be recommended. If methimazole is
used, the cat’s renal parameters must be closely evaluated in order to avoid any worsening of the renal
function. If this occurs, the methimazole must be discontinued or the dose decreased along with
continued close patient monitoring.
If the cat “passes” the Tapazole trial at the referring veterinarian’s practice, it will be admitted for I131
treatment. If there are no signs of cardiac disease, chances are no cardiac evaluation will be necessary. If
cardiac abnormalities are detected on our examination, a cardiac evaluation will be essential. If blood
pressure is > 160‐180, antihypertensive drugs will be considered either before or after treatment (if it
persists after treatment).
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