Radioiodine

Aka: Radioiodine, Radioactive Iodine, I-131

1. Indications
   1. Management of choice for Grave's Disease of all ages
   2. Recurrent Hyperthyroidism after Antithyroid Drugs
   3. Toxic Multinodular Goiter
   4. Toxic Nodule in patient over age 40 years
2. Contraindications
   1. Pregnancy
3. Pharmacokinetics
   1. Half-life of I-131: 9 days
   2. Effects nos seen for over 3-4 weeks
4. Mechanism
   1. Concentrates in and destroys Thyroid tissue
5. Precautions
   1. Background
      1. Radio-iodine excreted in urine, Saliva, feces
      2. Most is eliminated in first 48 hours
   2. For first 3 days
      1. Avoid contact with children and pregnant women
   3. For first few weeks
      1. Double flush toilet
      2. Wash hands carefully
6. Adverse Effects
   1. No increased risk of Cancer Death
   2. Radiation-Induced Thyroiditis
      1. Acute Thyroiditis in first 1-2 weeks post-I131
   3. Slight increased risk of Thyroid Cancer
      1. Graves Disease predisposes to Thyroid Cancer
      2. Cancers may have been present before I-131
   4. Graves Ophthalmopathy may worsen on I-131
      1. Occurs more commonly in Tobacco abuse
      2. Prednisone used to minimize this effect
         1. Dose: 40-80 mg daily
         2. Taper dose over 3 months
7. Efficacy: Euthyroid or Hypothyroid after symptoms
   1. Euthyroid at 6-8 weeks after I-131: 50 to 75%
   2. Euthyroid after one dose I-131: 80 to 90%
8. Follow-up
   1. Thyroid Stimulating Hormone every 6 weeks until stable
9. Protocols
   1. Beta Blockers control symptoms around radio-iodine
   2. Stop all meds containing iodine 2-3 weeks before iodine
   3. Concurrent use with Antithyroid Drugs (e.g. PTU)
      1. Indications
         1. Not indicated in most cases
         2. May be helpful in severe Hyperthyroidism
      2. Protocol near time of radio-iodine treatement
         1. Stop Antithyroid Drugs 3 days before radio-iodine
         2. Restart Antithyroid Drugs 3 days after radio-iodine
         3. Continue Antithyroid Drugs for 3 months then taper