Determining the breast-feeding interruption schedule after administration of 123I-iodide

Ann Nucl Med. 1998 Oct;12(5):303-6. doi: 10.1007/BF03164918.


Radioactivity after administration of 123I-sodium iodide was measured in breast milk samples obtained from a patient with postpartum thyroiditis. The breast milk was collected over 93 h during the infant's regular feeding times. The radioactivity in the breast milk was calculated with a 123I capsule of the same lot number as the standard source. 123I was excreted exponentially with an effective half-life of 5.5 h; 2.5% of the total radioactivity administered was excreted in the breast milk over the 93 h, 95% of which was excreted within the first 24 h, and 98.2% within 36 h. The first milk sample collected at 7 h after administration of the radiopharmaceutical contained 48.5% of the total radioactivity excreted. We estimated the potential absorption of radioactivity to an infant's thyroid in uninterrupted breast-feeding to be 30.3 mGy. With a 24-hour interruption, the absorbed radioactivity would be 1.25 mGy; with a 36-hour interruption, it would be 0.24 mGy. According to our calculations, breast feeding should be curtailed for 36 h to reduce the infant's exposure to 123I radioactivity. By using a correction factor based on maximum radioactivity from another 123I capsule of the same lot, we were able to ascertain the appropriate protocol for our patient and establish a measurement method that can be applied in similar clinical situations.

Publication types

  • Case Reports

MeSH terms

  • Adult
  • Breast Feeding*
  • Female
  • Half-Life
  • Humans
  • Infant, Newborn
  • Iodine Radioisotopes* / analysis
  • Iodine Radioisotopes* / pharmacokinetics
  • Metabolic Clearance Rate
  • Milk, Human / chemistry*
  • Puerperal Disorders / diagnostic imaging*
  • Puerperal Disorders / physiopathology
  • Radionuclide Imaging
  • Sodium Iodide / analysis
  • Sodium Iodide / pharmacokinetics
  • Thyroid Gland / diagnostic imaging*
  • Thyroiditis / diagnostic imaging*
  • Thyroiditis / physiopathology
  • Time Factors


  • Iodine Radioisotopes
  • Sodium Iodide