I-131- Medical Services

MedVet Memphis Radioactive Iodine Program

The Internal Medicine department at MedVet Memphis is excited to now be offering radioactive iodine therapy (I131) for the treatment of hyperthyroidism in cats.  As you know, this treatment modality has a success rate approaching 95% without the risks and inconveniences associated with either surgical (anesthesia, post-operative hypocalcemia, etc.) or oral anti-thyroid (i.e. methimazole) treatment (bone marrow suppression, hepatotoxicity, GI side-effects, pruritis).  Approximately 2.5% of I131-treated patients require a second treatment, and approximately 2.5% of patients develop post-treatment hypothyroidism that necessitates thyroid hormone supplementation.

The purpose of this letter is to inform you of our pre-treatment requirements.  Exceptions may be made in certain cases at the admitting doctor's discretion.  All cats referred for radioactive iodine treatment must make a routine appointment with the internal medicine service (specifically for I131 pre-evaluation) to discuss the risks and benefits of I-131 before scheduling the treatment - consultation and I-131 treatment cannot be done at the same time.  The cost of the initial appointment is payable regardless of whether the owner elects to pursue I131 therapy for their pet.  The total cost includes standard (usually 5 days) hospitalization, treatment, patient monitoring, litter kit and radioactive waste storage and decay.  Extended hospitalizations or other treatments may incur additional costs.
All cats must have the following diagnostic tests performed within 6 weeks of their referral appointment:

1) Complete blood count
2) Full chemistry profile (including BUN, creatinine, ALT/ALP, calcium, phosphorous, total protein, and electrolytes)
3) Urinalysis
4) T4 (+/- free T4)
5) Thoracic radiographs

Cats with cardiac murmurs or other abnormal findings on physical exam may require additional diagnostics, including systolic blood pressure, echocardiogram, etc.  Pre-treatment and post-treatment diagnostics are not included in the cost of treatment.

In addition, a 2-week oral methimazole trial is recommended for any cat with renal insufficiency (urine specific gravity < 1.025) that may be masked by the cat's hyperthyroid state.  Following the 2-week (or longer) trial, renal values and urine specific gravity should be rechecked.  Exceptions may be made on an individual basis in cases of methimazole hypersensitivity or fractious behavior, although the owner must be made aware of the risk of possible renal disease becoming apparent post-treatment.  It is recommended that all cats must be off methimazole for at least 1 week prior to I131 therapy.  Certain other supplements and medications may interfere with I131 treatment and should be avoided for at least a month, including (but not limited to) oral kelp, certain cough medicines, iodine containing vitamin/mineral supplements, water-soluble IV contrast agents, and anticholinergics (please contact us for a complete list).  Owners must realize that cats are kept in isolation in accordance with Tennessee state requirements for radioactive materials.  Isolation can last from 5-24 days after treatment.  Visitation is ABSOLUTELY NOT PERMITTED during that time.

A follow-up exam should be performed 4-6 weeks post treatment - a T4, urinalysis and BUN/creatinine and electrolytes should be rechecked at that time.  These laboratory tests should be repeated at 3 and 6 months post-treatment.

Please do not hesitate to call Drs. Sessions or Bayliss with any questions regarding this exciting treatment option for our feline patients.

Thank you,

MedVet Internal Medicine