Sodium Iodide I 131

Drug Levels and Effects:

Summary of Use during Lactation:

Elective diagnostic nuclear medicine procedures should be delayed until the patient is no longer breastfeeding.[1] Information in this record refers to the use ofsodiumiodide I 131 as a diagnostic and therapeutic agent. Breastfeeding should be discontinued permanently for this child after administration ofsodiumiodide I 131 in a dose of 0.01 MBq (0.004 mCi) or greater to a nursing mother.[2][3][4][5] Ceasing breastfeeding 6 weeks to 3 months before receiving a therapeutic dose ofsodiumiodide I 131 is recommended to reduce the radiation dose to the breasts and the risk of milk leakage that can contaminate clothing with radioactive iodine.[5] The American Thyroid Association recommends using I 123 or technetium scans for diagnosis of hyperthyroidism in nursing mothers.[6]

Parents should refrain from close contact with their infants after therapeutic iodine 131 administration. The exact duration depends on the dose administered, condition being treated, and source of the recommendation.[2][3][7] Recommended times range from 15 to 27 days after hyperthyroidism treatment, 16 to 24 days after ablation of thyroid cancer, and 4 to 5 days after follow-up therapy of thyroid ablation therapy.[3]

Drug Levels:

I 131 is a beta and high-energy gamma emitter with a main gamma emission energy of 364 keV and a physical half-life of 8.04 days.[2] The effective half-life ofsodiumiodide I 131 averages 9.2 hours (range 7.3 to 11.1 hours). Iodide is actively secreted into breastmilk and actively taken up by the mother's and infant's thyroid glands. From 25% to 46% of administered radioactivity is excreted into breastmilk after administration ofsodiumiodide I 131.[8]

Effects in Breastfed Infants:

Relevant published information was not found as of the revision date.

Possible Effects on Lactation:

Relevant published information was not found as of the revision date.

Alternate Drugs to Consider:

(Hyperthyroidism Diagnosis)SodiumPertechnetate Tc 99m,SodiumIodide I 123,(Hyperthyroidism Treatment) Propylthiouracil,Methimazole


1. Parker JA, Daube-Witherspoon ME, Graham LS, Royal HD, Todd-Pokropek AE, Yester MV. Procedure guideline for general imaging: 3.0. Society of Nuclear Medicine. 2004.
2. Howe DB, Beardsley M, Bakhsh S. Appendix U. Model procedure for release of patients or human research subjects administered radioactive materials. In, NUREG-1556. Consolidated guidance about materials licenses. Program-specific guidance about medical use licenses. Final report. U.S. Nuclear Regulatory Commission Office of Nuclear Material Safety and Safeguards. 2008;9, Rev. 2.
3. Anon. ICRP Publication 94. Release of patients after therapy with unsealed radionuclides. Ann ICRP. 2004;34:v-vi, 1-79. PMID:15571759
4. Mountford PJ, O'Doherty MJ . Exposure of critical groups to nuclear medicine patients. Appl Radiat Isot. 1999;50:89-111. PMID:10028630
5. Sisson JC, Freitas J, McDougall IR et al. Radiation safety in the treatment of patients with thyroid diseases by radioiodine 131I : practice recommendations of the American Thyroid Association . Thyroid. 2011;21:335-46. PMID:21417738
6. Stagnaro-Green A, Abalovich M, Alexander E et al. Guidelines of the American Thyroid Association for the diagnosis and management of thyroid disease during pregnancy and postpartum. Thyroid. 2011;21:1081-125. PMID:21787128
7. Siegel JA, Marcus CS, Stabin MG. Licensee over-reliance on conservatisms in NRC guidance regarding the release of patients treated with 131I. Health Phys. 2007;93:667-77. PMID:17993847
8. Mountford PJ, Coakley AJ. A review of the secretion of radioactivity in human breast milk: data, quantitative analysis and recommendations. Nucl Med Commun. 1989;10:15-27. PMID:2645546

Substance Identification:

Substance Name:

SodiumIodide I 131

CAS Registry Number:


Drug Class:

  • Radiopharmaceuticals

  • Iodine Radioisotopes

  • Administrative Information:

    LactMed Record Number:


    Last Revision Date:

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