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Radioiodine
Aka: Radioiodine, Radioactive Iodine, I-131
- Indications
- Management of choice for Grave's Disease of all ages (most common treatment in U.S.)
- Recurrent Hyperthyroidism after Antithyroid Drugs
- Toxic Multinodular Goiter
- Toxic Nodule in patient over age 40 years
- Contraindications
- Pregnancy
- Moderate or Severe Graves Orbitopathy, esp. Tobacco users
- Radioactive Iodine may worsen orbitopathy
- Mild Graves Orbitopathy may be concurrently treated with Corticosteroids
- Pharmacokinetics
- Half-life of I-131: 9 days
- Effects nos seen for over 3-4 weeks
- Mechanism
- Concentrates in and destroys Thyroid tissue
- Precautions
- Background
- Radio-Iodine excreted in urine, Saliva, feces
- Most is eliminated in first 48 hours
- For first 3 days
- Avoid contact with children and pregnant women
- For first few weeks
- Double flush toilet
- Wash hands carefully
- Adverse Effects
- No increased risk of Cancer Death
- Radiation-Induced Thyroiditis
- Acute Thyroiditis in first 1-2 weeks post-I131
- Slight increased risk of Thyroid Cancer
- Graves Disease predisposes to Thyroid Cancer
- Cancers may have been present before I-131
- Graves Ophthalmopathy may worsen on I-131
- Occurs more commonly in Tobacco Abuse
- Prednisone used to minimize this effect
- Dose: 40-80 mg daily
- Taper dose over 3 months
- Efficacy: Euthyroid or Hypothyroid after symptoms
- Euthyroid at 6-8 weeks after I-131: 50 to 75%
- Euthyroid after one dose I-131: 80 to 90%
- Labs
- Urine Pregnancy Test
- Obtain within 48 hours prior to Radioactive Iodine administration
- Protocols
- Stop all medications containing Iodine before Iodine (at least 2-3 weeks)
- Avoid large Iodine doses (e.g. iodinated contrast or Amiodarone) within 3 months prior to Radioiodine ablation
- Avoid pregnancy for 6 months after Radioiodine exposure
- Obtain Pregnancy Test within 48 hours of administration
- Management: Adverse Effects
- Beta Blockers control symptoms around radio-Iodine
- Concurrent use with Antithyroid Drugs (e.g. PTU, Methimazole)
- Indications
- Consider if on antithyroid medication prior to Radioiodine
- May be helpful in severe Hyperthyroidism
- Protocol near time of radio-Iodine treatement
- Stop Antithyroid Drugs 5 days before radio-Iodine
- Restart Antithyroid Drugs 3-5 days after radio-Iodine
- Continue Antithyroid Drugs for 3 months then taper
- Management: Follow-up
- Obtain Free T4 and Free T3 at 4-8 weeks after ablation and then every 8-12 weeks until stable
- Expect permanent Hypothyroidism at 2-6 months after Radioiodine ablation
- Initiate low dose Thyroid Replacement as Hypothyroidism develops
- References