What Is Iodine-131 or I-131?

Cats that have been diagnosed with hyperthyroidism can be treated with radioactive iodine, which has a high success rate at selectively destroying the overactive parts of the thyroid gland. The thyroid is the only tissue in the body that concentrates iodine. Radioactive iodine is administered by our trained and authorized radiology staff subcutaneously. route. The radioactive iodine will be concentrated in the abnormal thyroid tissue destroying it and allowing the normal thyroid tissue to begin functioning normally.

How is Hyperthyroidism Diagnosed?

The diagnosis of hyperthyroidism requires careful consultation with your veterinarian, who also should check your pet for other medical problems such as heart or kidney disease. Your veterinarian will order a blood test to check thyroid hormone levels and to detect overactivity in the thyroid gland.  

What is the Schedule for the Treatment?

Prior to I-131 treatment, our Internal Medicine specialist will meet with you and your cat. After the evaluation we will schedule the therapy. Typically, your hyperthyroid cat will be admitted on a Monday and the radioiodine treatment will be given that same day. Your pet will stay hospitalized until the end of the week. Although the majority of treated animals can go home Friday afternoon, occasionally a pet will have to remain in the hospital through the weekend so that the levels of radiation in their body has decreased sufficiently for release. While your pet is undergoing therapy, he will stay in a special, centrally located, radiotherapy hospital ward and be cared for by our authorized staff. Our i131 program is approved by the Nuclear Regulatory Commission and is overseen by both our Radiology and Internal Medicine Departments.

Guidelines for Home Care after Discharge

After your cat is treated with radioactive iodine (I-131) at The Central Hospital for Veterinary Medicine (CHVM) for the treatment of hyperthyroidism. He/she will have been housed at CHVM in a safe and secure environment while the radioactivity level has been high. When the levels are low enough he/she can go home to continue his/her recovery in your care. Because your cat still has radioactive material in his/her body, they continue to emit radiation. The level is low enough that no member of the public should be exposed to unhealthy levels of radiation (less than 100 mrem/year and less than 2 mrem per hour as defined by the Nuclear Regulatory Commission, as long as you follow the guidelines provided to you. This radioactivity will gradually decline and will be gone about 3 weeks after you take him/her home. During this time you must follow the safety procedures to minimize any risk of exposure to you or your family or others. If you have any questions or concerns, please do not hesitate to call us here at CHVM. Travel: The patient must be confined to a carrier at all times The carrier must have a waterproof bottom to avoid accidental urine leakage and contamination of the vehicle Public transportation may not be used to transport a patient who remains radioactive No one who is pregnant or under the age of 18 years may accompany the patient in the vehicle. The patient must be as far from the human occupants of the vehicle as possible to minimize exposure to humans Confinement: Your cat must be kept strictly indoors for 3 weeks For the first week, your cat must be isolated to a single room that will not be used by any person, such as an occupied bedroom or a frequented bathroom. After the first week, your cat may be given access to the remainder of the home. Contact: Please do not kiss your cat and avoid contact with your face for 3 weeks. Radioactive material is excreted in the cat’s saliva, which is then deposited onto its fur when they groom. This material is easily absorbed orally, and we do not want you or anyone else becoming contaminated. Wash your hands thoroughly after any contact with your cat, its food/water dishes, litterbox, and toys. No one under the age of 18 should be allowed to have access to your cat or the room in which it is isolated for the first week, and should avoid close contact (within 6 feet) for the subsequent 2 weeks. Pregnant women or women who are breastfeeding should not be allowed near the cat or the contaminated litter or bedding (within 6 feet) for 3 weeks. You may not allow your cat to sleep in your bed for 3 weeks. Keep your cat off the counters for 3 weeks to prevent the contamination of food-preparation surfaces. If this is not possible, make sure you clean any surfaces thoroughly before food preparation. Remember that minimizing contact and maximizing distance from your cat are the best ways to avoid radiation exposure. Personal contact must be restricted at first, but can be gradually increased over time based on the following Week 1 Close contact (within one foot) such as petting must be avoided completely Do not hold the cat or allow it to sit in your lap. The cat may not sleep in a bed with a person Maintain a distance of more than 3 feet from your pet Week 2 Petting is allowed, but should be limited to 20 minutes per day Wash hands after any direct contact Do not hold the cat or allow it to sit in your lap The cat may not sleep in a bed with a person At all other times maintain a distance of more than 3 feet Week 3 Petting is unrestricted Wash hands after any direct contact Laptime/holding should be limited to 30 minutes per day The cat may not sleep in a bed with a person Waste For 3 weeks, you should use plastic litter pan liners and flushable litter, and you should flush all waste. If flushing is not possible, all waste must be stored in an unused basement or garage. After this 3 weeks, take any stored or residual litter and double bag it. Leave it in an isolated corner of the garage or basement for another 2 weeks, then discard into the trash. You should wear protective gloves while cleaning the litter and wash your hands thoroughly afterwards. All cleaning rags, rubber gloves and other discarded material used to clean the animal’s litter box or contaminated surroundings (for example if they vomit or eliminate outside the litter box) should be treated as if they are contaminated as well, and kept with the bagged contaminated litter and held for the additional 2 weeks. Most landfills do not allow the disposal of low-level radioactive materials, and have sensitive equipment to detect its presence. To avoid being fined, please be sure to follow the above guidelines. Medical issues If you have any concerns about your pet’s response to the therapy or any other issues that develop during this period, please contact us at CHVM or your regular veterinarian as soon as possible. If your pet requires medical attention, we recommend that you bring him/her back to CHVM during their radioactive period. Our facilities are designed to safely house/hospitalized radioactive patients and our staff is trained to handle their special needs. If you return, please call ahead of time so that we may prepare for your arrival. If your cat requires medical attention and you wish to take him/her back to your regular vet during this time, call them first and explain the situation. Make sure you bring these instructions to give to your veterinarian. They can contact Dr. Harley or Dr. Rozear at CHVM for more information and safety instructions. Remember to keep your cat in his/her carrier at all times during transport. Follow up Please schedule a recheck visit with your veterinarian for 4-5 weeks after treatment to check the T4 level. If the thyroid is normal, you can resume routine care with your vet. If the T4 is low at this recheck, please schedule an additional follow up with your vet for 4-6 months for another T4.

Feline hyperthyroidism is one of the most common diseases of older cats, usually due to enlargement of the thyroid gland. The veterinarians of Central Hospital for Veterinary Medicine have experience in diagnosing and treating this disease, as well as the effective  radioactive iodine or I-131 treatment option.  I-131 treatment has advantages over medical and surgical treatments for feline hyperthyroidism.

  • No anesthesia is required
  • No daily medication
  • Returns thyroid function to normal usually within one month
  • Cost Effective
  • Does not have harmful side effects
      • Does not destroy healthy tissue
      • Does not damage other tissue or organs, including parathyroid glands