Sodium iodide ¹³¹I Other names: Sodium Iodide I-131

Risk Summary

Sodium iodide I 131 is contraindicated in pregnancy because fetal exposure can lead to neonatal hypothyroidism, which in some cases is severe and irreversible. Data from the published literature describe thyroid abnormalities after fetal exposure; including agenesis of the thyroid and hypothyroidism (see Data). No animal reproductive studies have been conducted.

Clinical Considerations

Fetal/Neonatal Adverse Reactions

A fetus exposed to sodium iodide I 131 can develop neonatal hypothyroidism. Delay in diagnosis of neonatal hypothyroidism after exposure to sodium iodide I 131 in utero can result in severe sequelae such as decreased mental capacity and delayed bone age. Monitor thyroid function in any infant born after in utero exposure to sodium iodide I 131.

Data

Human Data

Sodium iodide I 131 crosses the placenta and the fetal thyroid begins to concentrate iodide during the 10-12^th week of gestation. In literature reports of maternal exposures to sodium iodide I 131 at doses of 333–8325 MBq (9–225 mCi) during 4-26 weeks gestational age, the most common adverse outcomes were hypothyroid infants and children.

Risk Summary

Sodium iodide I 131 is contraindicated during lactation because I 131 concentrates in the breast during lactation via the increased expression of the sodium iodide symporter in breast tissue. If sodium iodide I 131 is administered in the postpartum period, the lactating mother should not breastfeed. In addition, to minimize the absorbed radiation dose to the breast tissue, breastfeeding and breast-pumping should be discontinued for at least 6 weeks before administration of sodium iodide I 131 (see Data). Women may breast feed with the birth of another child.

Infants exposed to sodium iodide I 131 through breast milk are at risk for development of hypothyroidism because sodium iodide I 131 is distributed into breast milk and may reach concentrations equal to or greater than concentrations in maternal plasma (see Data).

Data

Human Data

Limited published literature describes sodium iodide I 131 transfer into breast milk and thyroidal uptake by the breastfed infant. The amount of sodium Iodide I 131 detected in the breast milk at 36-48 hours after administration is 1-27% of the injected dose (with injected doses between 1.1–5143 MBq).

• Radiation-induced Thyroiditis
• Radiation-induced Toxicities
• Hypersensitivity Reactions
• Fetal Toxicity
• Increased Radiation Exposure to Breast Tissue with Lactation
• Transient Infertility
• Radiation Exposure

The following adverse reactions have been identified during post-approval use of sodium iodide I 131. Because these reactions are voluntarily reported by from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.

• Gastrointestinal disorders: sialadenitis, salivary gland dysfunction, nausea, vomiting, gastritis.
• Cardiac disorders: chest pain, tachycardia.
• Skin and subcutaneous tissue disorders: itching, rash, hives.
• Endocrine disorders: hypothyroidism, hyperthyroidism, thyrotoxic crisis, hypoparathyroidism
• General disorders and administration site conditions: local swelling of thyroid or sites of iodide avid tumor.
• Hematologic and lymphatic disorders including fatalities: bone marrow depression, anemia, leukopenia, thrombocytopenia, and blood dyscrasia.
• Neoplasms benign, malignant and unspecified (including cysts and polyps): acute leukemia, solid cancer.
• Eye disorders: lacrimal gland dysfunction.
• Congenital, familial and genetic disorders: congenital hypothyroidism, chromosomal abnormalities.
• Immune system disorders: bronchospasm.
• Nervous system disorders: headache, *cerebral edema.
• Respiratory, thoracic and mediastinal disorders: **radiation pneumonitis, **pulmonary fibrosis.

* In patients with iodide-avid brain metastases
** In patients with iodide-avid lung metastases