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Sodium Iodide I 123 use while Breastfeeding

Drugs containing Sodium Iodide I 123: ARI Sodium Iodide (I123) 1-12 MBq, ARI Sodium Iodide (I123) 100-750 MBq

Medically reviewed by Last updated on Dec 4, 2018.

Sodium Iodide I 123 Levels and Effects while Breastfeeding

Summary of Use during Lactation

Information in this record refers to the use of sodium iodide I 123 as a diagnostic agent. Considerable controversy exists in the literature concerning the breastfeeding interruption time after the diagnostic use of sodium iodide I 123, partly depending on assumptions used for the levels of impurities, especially I 125, in commercial products. The International Commission on Radiological Protection states that breastfeeding should be interrupted for more than 3 weeks following diagnostic use of sodium iodide I 123. This usually will result in permanent discontinuation of breastfeeding for this infant.[1] However, other experts recommend much shorter times. Recent information indicates that I 125 contamination is currently much less than earlier estimates.[2] The American Thyroid Association recommends discontinuation of breastfeeding for only 3 to 4 days after a diagnostic scan.[3] The safest course of action may be to have breastmilk tested at a nuclear medicine facility at a hospital. When the radioactivity is at a safe level the mother may resume breastfeeding. A method for measuring milk radioactivity and determining the time when a mother can safely resume breastfeeding has been published.[4] Mothers who receive a dose less than 400 MBq for a thyroid scan need not refrain from close contact with their infants.[5]

Drug Levels

I 123 is a gamma emitter with a principal photon energy of 159 keV and a physical half-life of 13.2 hours.[6] Iodide is actively secreted into breastmilk and actively taken up by the mother's and infant's thyroid glands. The effective half-life of I 123 is 5.8 hours.[4][7]

Maternal Levels. A lactating woman was administered 270 microcuries of NaI 123. The estimated level of contamination with I 125 in one breastmilk sample was 1.2 pCi/mL.[2]

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

Effects in Breastfed Infants

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

Effects on Lactation and Breastmilk

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

Alternate Drugs to Consider

(Hyperthyroidism Diagnosis) Sodium Pertechnetate Tc 99m


1. Mattsson S, Johansson L, Leide Svegborn S et al. Radiation dose to patients from radiopharmaceuticals: A compendium of current information related to frequently used substances. Annex D. Recommendations on breast-feeding interruptions. Ann ICRP. 2015;44 (2 Suppl):319-21. PMID: 26069086

2. Lofton B, Gibbs G, Stickel J et al. Measured I-125 contamination in I-123. Med Phys. 2017;44:3127. Abstract. DOI: doi:10.1002/mp.12304

3. Alexander EK, Pearce EN, Brent GA et al. 2016 Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease during Pregnancy and the Postpartum. Thyroid. 2017;27:315-89. PMID: 28056690

4. Stabin MG, Breitz HB. Breast milk excretion of radiopharmaceuticals: mechanisms, findings, and radiation dosimetry. J Nucl Med. 2000;41:863-73. PMID: 10809203

5. Mountford PJ, O'Doherty MJ. Exposure of critical groups to nuclear medicine patients. Appl Radiat Isot. 1999;50:89-111. PMID: 10028630

6. 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.

7. 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

Sodium Iodide I 123 Identification

Substance Name

Sodium Iodide I 123

CAS Registry Number


Drug Class

Breast Feeding



Iodine Radioisotopes

Administrative Information

LactMed Record Number



Information presented in this database is not meant as a substitute for professional judgment. You should consult your healthcare provider for breastfeeding advice related to your particular situation. The U.S. government does not warrant or assume any liability or responsibility for the accuracy or completeness of the information on this Site.

Further information

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