For an adult non‑pregnant, non‑lactating patient with confirmed hyperthyroidism (elevated free T4/T3, suppressed TSH) and no severe active Graves ophthalmopathy, what are the indications, recommended I‑131 (Sodium‑131) dose, pre‑treatment preparation, contraindications, radiation safety instructions, and follow‑up monitoring?

I-131 Treatment for Hyperthyroidism

For confirmed hyperthyroidism without severe active Graves' ophthalmopathy, I-131 therapy is indicated with a typical dose of 4-10 mCi for Graves' disease or toxic nodular goiter, administered after discontinuing antithyroid drugs 3-4 days prior, with mandatory pregnancy exclusion and contraception for 6-12 months post-treatment. 1

Indications for I-131 Therapy

• I-131 is indicated for hyperthyroidism caused by Graves' disease, toxic multinodular goiter, and toxic adenoma in adults. 1, 2
• The FDA label specifies that I-131 is not usually used for hyperthyroidism treatment in patients under 30 years of age. 1
• I-131 can be considered first-line therapy for small-to-medium sized thyroid glands in Graves' disease. 2

Absolute Contraindications

• Pregnancy is an absolute contraindication—verify negative pregnancy test before administration. 1
• Active breastfeeding is contraindicated; breast feeding must be discontinued during and following dose administration. 1
• Severe active Graves' ophthalmopathy is a relative contraindication, as I-131 may induce or worsen ophthalmopathy (preventable with corticosteroids). 3

Pre-Treatment Preparation

Antithyroid Drug Management

• Discontinue antithyroid drugs (methimazole, propylthiouracil) 3-4 days before I-131 administration to optimize thyroid uptake. 1
• Beta-blockers should be continued for symptomatic control and can be safely used throughout treatment. 4

Iodine Avoidance

• Avoid iodinated contrast agents before I-131 therapy, as they interfere with radioiodine uptake. 5
• Implement a low-iodine diet for 1-2 weeks prior to treatment to maximize thyroid uptake (though not explicitly required by FDA label for hyperthyroidism). 1

Laboratory Confirmation

• Confirm elevated free T4/T3 and suppressed TSH before proceeding. 4
• Obtain baseline complete blood count, as bone marrow depression is a potential side effect. 1

Recommended I-131 Dosing

Standard Dosing Protocol

• For Graves' disease and toxic nodular goiter: 4-10 mCi is the usual dose range. 1
• For toxic nodular goiter and special situations: larger doses may be required. 1
• A mean dose of 10 mCi shows great effectiveness, with 75% of patients cured after one administration and 88% after two doses. 2

Dose Calculation Considerations

• Calculated doses based on gland size and radioiodine turnover can achieve higher rates of long-term euthyroidism compared to fixed dosing. 2
• Larger glands, accelerated intra-gland radioiodine turnover, presence of ophthalmopathy, and recent antithyroid drug use are associated with higher failure rates. 2

Radiation Safety Instructions

Patient Instructions

• Maintain distance from pregnant women and young children (>3 feet) for 3-7 days post-treatment. 6
• Sleep alone for 3-7 days after treatment. 6
• Use separate bathroom facilities if possible; flush toilet 2-3 times after each use. 6
• Wash hands thoroughly and frequently. 6
• Use separate eating utensils and wash them separately. 6
• Wash clothing and linens separately from others for the first week. 6

Healthcare Personnel Safety

• Waterproof gloves must be used during the entire handling and administration procedure. 1
• Adequate shielding must be maintained at all times. 1
• Minimize time of exposure, maximize distance from the radiation source, and use appropriate shielding. 6

Post-Treatment Monitoring Protocol

Early Follow-Up (First Year)

• Monitor thyroid function tests (TSH, free T4, free T3) at 1,2,3,6, and 12 months post-treatment. 2, 4
• Transient increases in thyroid hormone levels may occur in the first week (especially in toxic multinodular goiter), but clinically significant exacerbations are rare with beta-blocker coverage. 4
• 84.1% of treatment failures occur within the first year (mean 0.34±0.23 years). 2

Hypothyroidism Surveillance

• 39.8% of patients who develop hypothyroidism are diagnosed within the first year. 2
• After the initial sharp rise, hypothyroidism occurs at an estimated yearly rate of 3.8% until 10 years and 1.8% thereafter. 2
• Long-term euthyroidism is maintained in approximately 50% of patients at 10 years and one-third at 25 years. 2

Long-Term Monitoring

• Continue annual thyroid function testing indefinitely, as hypothyroidism can develop years after treatment. 3
• Monitor for rare complications including salivary gland dysfunction (sialitis), though this is more common in thyroid cancer patients receiving higher doses. 3

Common Pitfalls and Caveats

Treatment Failure Risk Factors

• Failure to discontinue antithyroid drugs 3-4 days before treatment reduces efficacy. 2
• Larger goiter size and accelerated radioiodine turnover increase failure risk—consider higher doses in these patients. 2
• Presence of ophthalmopathy is associated with higher failure rates. 2

Ophthalmopathy Management

• In patients with mild Graves' ophthalmopathy, consider prophylactic corticosteroids (e.g., prednisone 0.3-0.5 mg/kg/day for 1-3 months) to prevent worsening. 3
• Avoid I-131 in severe active ophthalmopathy until inflammation is controlled. 3

Contraception Requirements

• Women of childbearing potential must use effective contraception for 6-12 months after I-131 therapy. 1
• Men should also practice contraception for 4-6 months post-treatment to avoid potential genetic effects. 3

Potential Adverse Effects

• Radiation sickness, bone marrow depression, acute leukemia, anemia, chromosomal abnormalities, acute thyroid crisis, blood dyscrasias, leukopenia, thrombocytopenia, and death represent potential side effects, though reactions are rare. 1
• No definitive evidence exists for increased overall cancer risk, though some studies suggest possible increased relative risk for specific cancers (thyroid, stomach, bladder, kidney, hematological malignancies) that were not confirmed in other large studies. 3