Sodium Iodide I-131 (3 brand names, 2 dosage forms, 1 route)
Available dosage forms: CAPSULE, SOLUTION.
Routes of administration: ORAL.
Brand Names
- HICON
- IODOTOPE
- SODIUM IODIDE I 131
Related Health Topics
Indications and Usage
Sodium Iodide I-131 Solution is indicated for the treatment of hyperthyroidism and selected cases of thyroid carcinoma.
Contraindications
Sodium Iodide I-131 is contraindicated in: Patients with vomiting and diarrhea [see Warning and Precautions (5.7)] . Patients with thyroid malignancies shown to have no iodide uptake, which include the majority of medullary or anaplastic carcinomas. Patients receiving concurrent anti-thyroid therapy [see Warning and Precautions (5.1) and Drug Interactions (7)] . Pregnancy [see Warnings and Precautions (5.4), see Use in Specific Populations (8.1)] . Lactation [see Warnings and Precautions (5.5)] .
Adverse Reactions
The following clinically significant adverse reactions are described below and elsewhere in labeling: Radiation-induced Thyroiditis [see Warnings and Precautions (5.1)] . Radiation-induced Toxicities [see Warnings and Precautions (5.2)]. Hypersensitivity Reactions [see Warnings and Precautions (5.3)]. Embryo-Fetal Toxicity[see Warnings and Precautions (5.4), Use in Specific Population (8.1)]. Increased Radiation Exposure to Breast Tissue with Lactation [see Warnings and Precautions (5.5), Use in Specific Populations (8.2) ]. Transient Infertility [see Warnings and Precautions (5.6), Use in Specific Population (8.3) ]. Radiation Exposure to Other Individuals [see Warnings and Precautions (5.7)]. Risk of Decreased Effectiveness of Therapy [see Warnings and Precautions (5.8)].
Drug Interactions
Concomitant use of bone marrow depressants may enhance the depression of the hematopoietic system caused by the use of large doses of sodium iodide I 131 [see Warnings and Precautions (5.2)] . Many drugs and iodide-containing foods interfere with the accumulation of radioiodide by the thyroid. Review the patients history, current medications, and recent diagnostic tests prior to the administration of sodium iodide I 131 [see Warnings and Precautions (5.8)] . Advise patients to maintain a low-iodide diet two weeks prior to radioiodide administration and continue for several days during the uptake or imaging process and to discontinue taking the following products before they undergo the procedure as shown in Table 4. Table 4 Pharmaceuticals/OTCs/Agents Blocking Radioiodine Uptake Type of Medication Recommended time of withdrawal Thionamide medications (e.g., propylthiouracil, methimazole, carbimazole) 3 days Multivitamins containing iodide 10 days Natural or synthetic thyroid hormones triiodothyronine thyroxine 2 weeks 4 weeks Iodide-containing foods: iodized salt, dairy products, egg yolks, seafood, turkey and liver 2 weeks Kelp, agar, carrageenan, Lugol solution 3 weeks Saturated solution of potassium iodide 3 weeks Topical iodide (e.g., surgical skin preparation) 3 weeks Intravenous radiographic contrast agents Water soluble Lipophilic 2 months 6 months Amiodarone 6 months
Mechanism of Action
Iodide is actively transported by the sodium-iodide symporter (NIS) protein, in thyroid follicular cells. Iodide is concentrated in follicular cells to levels up to 50 times higher than in the plasma. Iodide is metabolically oxidized by thyroid peroxidase to iodinium (I +) which in turn iodinates tyrosine residues of thyroglobulin (tri or tetra-iodinated tyrosine). The beta emission of I 131 is responsible for the therapeutic effect.
Overdosage
In case of exposure to a radioactive dose of sodium iodide I 131 exceeding the intended therapeutic dose, provide general supportive care, promote frequent voiding, monitor for bone marrow and thyroid suppression. Consider administering a thyroid blocking agent (e.g. potassium iodide (KI) or perchlorate) promptly within 4 to 6 hours after the exposure. Assess the benefit of administering a thyroid blocking agent against the risk of failure of sodium iodide I 131 therapy. Appropriate replacement therapy is recommended if hypothyroidism occurs.