Radioactive Iodine FAQs

Methimazole was developed for human use in hyperthyroid patients who were diagnosed during pregnancy, on a short waiting list for radioactive iodine treatment, or terminally ill. It was never intended for long term use, not even in humans. Methimazole does not stop the growth of the thyroid tumor, has a short drug half-life of effectiveness, and has an extremely high rate of drug reactions. Over 20% of patients cannot tolerate this medication. As the tumor grows and the level of thyroid hormones rises, progressive damage to all organs of the body dramatically increases. The heart and kidneys take the biggest hits from hyperthyroidism, so the earlier the disease is diagnosed and cured, the better the outcome for the patient. Radio-iodine in human and in veterinary medicine is the gold standard of care, and all other therapies are much less effective and/or dangerous. Studies have shown that radio-iodine patients live 2-3 times longer than methimazole treated patients, while the overall costs are 2-4 times higher for methimazole treated patients.

A current blood chemistry profile and blood pressure are needed. The blood chemistry must include a T4 or T4 and Free T4 (for borderline cases) which is run at a reference (outside) lab. This result typically takes about two days. If your veterinarian has referred to us before, he or she is already very familiar with these requirements. And if your veterinarian is the one referring your cat, it is 99% likely that these tests have already been completed.

We do not require vaccinations for hyperthyroid cats undergoing radio iodine treatment, but we do recommend having your pet up to date on their Rabies and FVRCP vaccines for optimum protection.

Hyperthyroidism as it progresses causes the liver to be overworked and become damaged. Additionally, 20% of patients who have received methimazole become sick and have rising liver enzymes. Most elevated liver enzymes are associated with the rise in thyroid hormones, and go back to normal after radio-iodine treatment. It is uncommon in hyperthyroid patients to have primary liver disease. Separating primary and secondary liver disease is extremely difficult. The odds favor curing the hyperthyroidism and having both diseases resolve. If a primary liver problem remains, it should be worked up as a separate, underlying disease.

Hyperthyroidism is a major endocrine disease that can be cured. Radio-iodine therapy is the gold standard in human and in veterinary medicine, and is very cost effective. Compare the costs and continued costs of medically treated hyperthyroidism, thyroid surgery, twice daily insulin treatments for diabetes, fractured limb repairs, treating congestive heart failure, treating chronic liver and kidney disease and then compare the curing of hyperthyroidism. The cost to value ratio is amazing. When was the last time you heard the word “cure” used with any major, chronic medical condition?

It is given as a subcutaneous injection, similar to a vaccine. It is not injected into the thyroid gland. Within 20 minutes the radio-iodine dose is being absorbed into the bloodstream and is targeting the thyroid gland in the neck. Active thyroid tissue is the only tissue that concentrates radio-iodine. No other tissue is affected.

On Tuesdays, so that most of our patients can go home the same week. 

Hyperthyroidism is a multi-systemic disease that affects all organs of the body – from the brain to the tip of the tail and everything in between. It severely damages the heart, kidneys and liver by making these organs work harder and work overtime. The body can’t rest, and a negative metabolic state becomes normal. The end result can be total heart failure, kidney failure, liver failure, and the collapse of all systems. It is a common misconception that methimazole will stop this. Its effect is partial at best. Methimazole masks the symptoms of hyperthyroidism, while the tumor continues to grow and the disease continues to advance. Dosage of methimazole needs to be continually monitored. It must be increased or in some cases decreased or stopped as the disease continues to advance until many cats cannot be controlled with medication. When the cats become intolerant to methimazole, these patients are sick and can only be saved with radio-iodine. These are very high risk patients with questionable outcomes. Treat early for a cure!