Feline Radioactive Iodine Therapy

Feline Radioactive Iodine TherapyRadioactive iodine (I-131) is widely considered the safest, simplest and most effective form of treatment for feline hyperthyroidism.  Cure is obtained in over 90% of cases following a single treatment, side-effects are negligible and general anaesthesia, surgery or ongoing medications are not required.

At Adelaide Veterinary Specialist & Referral Centre we have been successfully treating hyperthyroid cats with I-131 for over eight years. 95% of owners of cats treated between 2004 and 2010 surveyed indicated they were satisfied with their cat’s treatment and 86% indicated they would recommend I-131 treatment to others. 

Treated cats must be hospitalised in a radiation isolation ward for an average of eight days after treatment and are subject to further indoor isolation and special handling precautions for two weeks at home after discharge. Clients are provided with full written instructions regarding special handling of treated cats and their wastes after treatment.

A consultation is necessary before ordering I-131 to assess the suitability of individual cats for treatment. Affected cats are older (average age twelve years) and may have concurrent disease or complications of hyperthyroidism that affect their suitability for isolation. Evaluation for kidney and heart disease is particularly important and is recommended in all cases. 

All cats treated for hyperthyroidism – by any method – experience a measurable decrease in kidney function after treatment. In many cases kidney function is merely returning to normal from a high baseline, but in some cases kidney failure may be “unmasked” after treatment. Cats that develop low thyroid hormone (T4) after treatment may be at increased risk of developing kidney failure. An individualised dose of I-131 is therefore determined by the specialist for each patient; optimising the dose minimises the risk of treatment failure and of T4 falling below normal. 

For cats suspected of pre-existing kidney disease from blood or urine tests a period of reversible medical treatment with carbimazole tablets or transdermal methimazole gel followed by re-evaluation of kidney function may be recommended; these medications should be withdrawn one-two weeks before I-131 treatment. A short course of thyroxine following I-131 treatment may also aid in protecting the kidneys in at-risk cats.