Client information guide
Radioactive iodine (I-131) treatment for feline hyperthyroidism
Information for cat owners from The Narre Warren Vet.
What is radioactive iodine (I-131)?
Radioactive iodine (I-131) is considered the gold standard treatment for feline hyperthyroidism. It is a safe, highly effective treatment that selectively destroys overactive thyroid tissue while preserving normal thyroid tissue.
At our hospital, radioactive iodine is administered as a single oral capsule. The capsule is absorbed naturally and concentrates within the abnormal thyroid tissue, where it destroys the overactive cells while having minimal effect on the rest of the body.
Unlike oral anti-thyroid medication, which only controls thyroid hormone production, I-131 treats the underlying disease and provides a permanent cure for most cats.
Why choose radioactive iodine?
Compared with lifelong medication, I-131 offers many advantages:
- Gold standard treatment for feline hyperthyroidism.
- Treats the underlying disease rather than simply controlling it.
- No ongoing tablets or daily medication.
- Avoids the long-term side effects associated with anti-thyroid medication.
- Eliminates the need for lifelong prescription medication and dose adjustments.
- Improves quality of life for both cats and their owners.
Success rates
Radioactive iodine has an excellent success rate.
- Over 95% of cats are successfully cured with a single radioactive iodine treatment.
- Approximately 1-2% of cats may remain hyperthyroid and require a second treatment.
- Approximately 1-2% of cats may develop hypothyroidism (an underactive thyroid) following treatment. If this occurs, it is usually straightforward to manage with thyroid hormone supplementation.
- Some cats may have underlying kidney disease that only becomes more apparent after thyroid hormone levels return to normal. This is why thorough screening before treatment and follow-up blood tests are essential.
Is my cat a candidate?
Before booking treatment, your cat’s records will be assessed by our attending veterinarians to ensure radioactive iodine is the most appropriate option.
Suitable candidates generally require:
- A confirmed diagnosis of hyperthyroidism and your cat must have had at least 4 weeks on hyperthyroid medication.
- Recent blood tests, including thyroid hormone (T4) levels. These tests should be performed before and after that hyperthyroid medication trial (of at least 1 month or more).
- Urine testing (before and after treatment).
- Stable overall health.
- No significant concurrent illnesses that would make treatment unsuitable.
Additional investigations, such as blood pressure measurement or cardiac assessment, may be recommended by your regular veterinarian.
The treatment process
Step 1: Initial enquiry
Cat owners can contact us directly to register interest, or your regular veterinarian can submit a referral.
We require your cat’s full medical history and all relevant blood and urine test results.
Our attending veterinarian will review the information and determine whether your cat is a suitable candidate for treatment.
Step 2: Phone consultation
If your cat is deemed a suitable candidate for radioactive iodine treatment, we will arrange a complimentary phone consultation with our attending vet. Our vet will go through the treatment process in more detail and answer any further questions that you might have.
If you choose to proceed, we do require a non-refundable deposit of $1000.
Step 3: Two weeks before admission
Two weeks before your scheduled admission, you will receive a reminder email with preparation instructions.
Thyroid medication
All anti-thyroid medication must be stopped 14 days before admission.
This allows the abnormal thyroid tissue to absorb the radioactive iodine effectively, maximising the success of treatment.
What to bring
Please bring:
- Seven (7) days of your cat’s usual food to help maintain familiarity and minimise dietary changes during hospitalisation.
- Non-returnable bedding or comfort items, such as a towel, blanket or small toy that smells like home.
Please note that any bedding or comfort items brought into the radioactive ward cannot be returned after treatment due to radiation safety regulations.
Step 4: Admission day
You will be booked in with our attending veterinarian for an admission appointment.
During admission, we will perform a physical examination.
The radioactive iodine treatment is given the following day.
Step 5: Treatment and hospitalisation
The radioactive iodine treatment requires a mild sedation to ensure proper administration.
Following treatment, your cat must remain in our licensed radioactive iodine facility while radiation levels naturally decrease.
For most cats, hospitalisation is typically 7 days. On the final day, we measure the radiation levels to ensure they are safe to leave isolation.
During their stay your cat will receive:
- Daily veterinary supervision.
- Regular feeding.
- Monitoring of appetite, behaviour and overall wellbeing.
- Any additional medical treatment if required.
Unfortunately, Australian radiation safety regulations do not permit owner visitation during hospitalisation.
Step 6: Going home
Your cat can be discharged once radiation levels have fallen below the legal release limit.
Before discharge, we will discuss your home-care instructions in detail and answer any questions you may have.
Home care after discharge
For two weeks after discharge, your cat should remain on a temporary “semi-quarantine.”
These precautions help minimise radiation exposure while the remaining radioactivity naturally decays.
During this period we recommend:
- Keeping your cat indoors where possible.
- Avoiding prolonged close physical contact (no more than 10 minutes per day).
- Avoiding sleeping with your cat.
- Limiting cuddling to short periods.
- Washing hands thoroughly after handling your cat or litter.
- Following the litter disposal instructions provided at discharge.
- Avoid any contact with pregnant women or children.
These precautions are temporary and will be explained in detail before your cat goes home.
Next steps
Follow up blood tests with your regular vet are required:
- 6 weeks after treatment
- 3 months after treatment
A referral report will be sent directly to your regular veterinarian, but we ask clients to contact their regular vet directly to book their follow up blood testing.
Frequently asked questions
Is the treatment painful?
No. Radioactive iodine is administered as a single oral capsule and is generally very well tolerated.
Will my cat need medication afterwards?
Most cats will not require any further thyroid medication after successful treatment.
My cat has just been diagnosed with hyperthyroidism, can I start radioactive iodine treatment immediately?
No. We require cats to be treated with anti-thyroid medication for at least four weeks before they are considered for radioactive iodine (I-131) treatment.
There are several reasons for this:
- Not all cases of feline hyperthyroidism are the same. A trial of anti-thyroid medication helps us assess how your cat responds to treatment and can provide valuable information about the nature of their thyroid disease.
- Hyperthyroidism can mask other health conditions, particularly kidney disease. High thyroid hormone levels increase blood flow to the kidneys, which can make kidney function appear better than it actually is.
- Once thyroid hormone levels are controlled with medication, we can perform repeat blood and urine testing to determine whether any underlying conditions become apparent before proceeding with radioactive iodine treatment.
- Ensuring your cat is medically stable before treatment helps maximise safety and improves the likelihood of a successful outcome.
What if the treatment doesn't work?
Approximately 1-2% of cats remain hyperthyroid after treatment and may require a second radioactive iodine treatment.
Can my cat become hypothyroid?
There is a 1-2% risk of developing hypothyroidism (low thyroid) following treatment. If this occurs, it can usually be managed successfully with thyroid hormone supplementation.
Why can't I visit my cat?
Australian radiation safety regulations require cats receiving radioactive iodine treatment to remain isolated until radiation levels have fallen below the legal discharge limit.
When will I notice improvement?
Most cats begin to show improvement over the weeks following treatment. As thyroid hormone levels return to normal, owners commonly notice:
- Gradual weight gain.
- A healthier coat.
- Reduced appetite and thirst.
- Less vomiting.
- Improved energy levels and behaviour.
Questions?
Please don’t hesitate to contact us. We’re here to help guide you through every step of the process. You can submit an enquiry here.
Talk to our team
Questions about radioactive iodine treatment? We are happy to help.
Radioactive iodine
Overview
Information for cat owners
Information for vets
Enquiry form
Ready to book a visit?
Book online in a few clicks or call our friendly team. We look forward to meeting you and your pet.