Northern California Veterinary Specialists, Inc.

Systemic administration of organ-seeking radioactive1 pharmaceuticals is a common application of nuclear medicine in veterinary medicine.  This form of treatment is limited to specific tumors that have the potential to concentrate the radioactive substance.
Radioactive iodine (131I) is the most common  radiopharmaceutical in cats and dogs.  Because radioactive iodine (131Iodine) is metabolized and accumulates only in the thyroid gland tissues like stable iodine to produce thryoid hormone, it is used for the treatment of hyperthyroidism and thyroid cancer, especially in cats. 

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