I-131

Effective Treatment of Feline Hyperthyroidism with I-131

Feline hyperthyroidism is one of the most common diseases of older cats, usually due to enlargement of the thyroid gland. The veterinarians of Red Bank Veterinary Hospitals have experience in diagnosing and treating this disease, as well as the effective treatment option radioactive iodine or I-131.

Diagnosing Feline Hyperthyroidism

Symptoms of feline hyperthyroidism include weight loss, ravenous appetite, gastrointestinal signs, and hyperactivity. Excessive thyroid hormone affects every organ, leading to heart conditions and high blood pressure.

To diagnose feline hyperthyroidism, a thyroid hormone level blood test known as a T4 is performed. Some cats require additional blood testing or repeated thyroid levels.

Comprehensive Treatment

Therapies for hyperthyroidism include prescription diet, oral medication, removal of the thyroid gland, and radioactive iodine treatment.

  • Diet—An iodine-restricted prescription diet must be the only food given for effective reduction of the thyroid level. This treatment is not recommended in cats with pre-existing renal disease.
  • Oral medication—Methimazole reduces production of thyroid hormone when given twice daily in tablet form or compounded into a transdermal formulation. Gastrointestinal upset is common; less common side effects include liver toxicity, skin lesions, and decreased red blood cells and platelets. Side effects typically resolve when medication is stopped.
  • Surgery—Removal of the thyroid gland is rarely recommended. Although the surgery is fairly simple, anesthesia on an older hyperthyroid cat is considered high risk. Complications related to calcium regulation may also occur in the post-operative period.
  • Radioactive iodine—I-131 is an extremely effective therapy. In the body, iodine is naturally absorbed by the thyroid gland. Radioactive iodine is injected under the skin; the radioactivity is absorbed and destroys the abnormal thyroid cells, a permanent correction of hyperthyroidism. The patient is hospitalized for four to five days so levels of radioactivity can be measured. Once the level reaches an acceptable low range, the patient discharged.

Effectiveness of I-131

The response rate to I-131 therapy is excellent. Of all cats treated, 94% require only one injection and less than 3% need follow-up treatment. Hypothyroidism, a low level of thyroid hormone, is a rare side effect of using radioactive iodine. If a cat develops hypothyroidism as a result of treatment, medication can easily correct the thyroid level.

I-131 Appointments

If you are interested in radioactive iodine treatment for your cat, please speak with your primary care veterinarian or contact Red Bank Veterinary Hospitals Internal Medicine Department at (732) 747-3636.

Patients are scheduled for admission and treatment on Mondays and are typically discharged on Fridays. While your cat is with us, we call you with daily updates and send daily updates to your primary care veterinarian.

Radioactive iodine is prescribed specifically for each cat and ordered when you schedule treatment. This order can only be cancelled by 3 p.m. on the Friday prior to the scheduled treatment.

Meet our I-131 Team


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