Determining the breast-feeding interruption schedule after administration of 123I-iodide.
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.
Morita
S
S
Department of Radiology, Kurume University Hospital, Japan. smorita@med.kurume-u.ac.jp
Umezaki
N
N
Ishibashi
M
M
Kawamura
S
S
Inada
C
C
Hayabuchi
N
N
D000328:Adult; D001942:Breast Feeding; D005260:Female; D006207:Half-Life; D006801:Humans; D007231:Infant, Newborn; D007457:Iodine Radioisotopes / Q000032:analysis / Q000493:pharmacokinetics; D008657:Metabolic Clearance Rate; D008895:Milk, Human / Q000737:chemistry*; D011644:Puerperal Disorders / Q000000981:diagnostic imaging* / Q000503:physiopathology; D011877:Radionuclide Imaging; D012974:Sodium Iodide / Q000032:analysis / Q000493:pharmacokinetics; D013961:Thyroid Gland / Q000000981:diagnostic imaging*; D013966:Thyroiditis / Q000000981:diagnostic imaging* / Q000503:physiopathology; D013997:Time Factors
D007457:Iodine Radioisotopes; D012974:Sodium Iodide