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VARIOUS › DIAGNOSTIC RADIOPHARMACEUTICALS › THYROID › Various thyroid diagnostic radiopharmaceuticals
sodium iodide (131I)
V09FX03
Forms & Strengths
- Oral solution: Carrier-free Na131I in varying diagnostic/therapeutic activities
- Capsules: Gelatin capsules containing Na131I for oral administration
Adult Dosing
- Hyperthyroidism (Graves' disease): Typically 400-800 MBq (10-21.6 mCi) administered as a single oral dose
- Thyroid carcinoma (remnant ablation/metastases): 1,850 - 5,550 MBq (50 - 150 mCi) administered orally
Pediatric Dosing
- Hyperthyroidism: Dosing is individualized based on gland size, 24-hour RAIU, and body weight; generally lower calculated activities than adults
- Thyroid carcinoma: Safety and efficacy in pediatric patients are less well established; individualized calculations based on body surface area or weight
Indications
- Treatment of hyperthyroidism (Graves' disease, toxic multinodular goiter)
- Ablation of thyroid tissue post-thyroidectomy for well-differentiated thyroid carcinoma
- Treatment of residual or metastatic thyroid carcinoma
Mechanism of Action
- Active transport of iodide (131I) into thyroid follicular cells via the sodium-iodide symporter (NIS)
- Emits beta particles (destructive to local thyroid tissue via cellular radiation damage) and gamma rays (used for imaging)
Contraindications
- Pregnancy (causes fetal thyroid destruction and irreversible hypothyroidism)
- Breastfeeding (requires cessation of nursing)
- Vomiting or severe diarrhea (risk of emetic spread of radioactivity)
Adverse Reactions
- Radiation thyroiditis (neck swelling, pain, tenderness)
- Transient hypothyroidism
- Permanent hypothyroidism (often intentional in hyperthyroidism treatment)
- Sialadenitis (salivary gland inflammation, dry mouth, taste alteration)
- Bone marrow suppression (at high therapeutic doses for cancer)
- Secondary primary malignancies (rare, at very high cumulative doses)
Drug Interactions
- Antithyroid drugs (methimazole, propylthiouracil): Deplete thyroid iodine stores; should be withheld several days before administration
- Thyroid hormones (levothyroxine, liothyronine): Suppress TSH and reduce 131I uptake; withdraw prior to therapy
- Iodine-containing medications, contrast agents, and kelp: Competitively block radioactive iodine uptake; withhold for weeks prior to administration
- Lithium: May prolong the retention of 131I within the thyroid gland
Curated Content: Needs Vetting Before Put to Clinical Use