The water-soluble iodine-containing contrast media, meglumine amidotrizoate and sodium amidotrizoate, iodamide, iohexol, and rnetrizamide, appear in the milk of a fully breastfed infant in a relative dose considerably under 1% (Nielsen 1987, Texier 1983, Fitzjohn 1982, Ilett 1981).The portion of free iodine in contrast media is under O.I°/o of the total amount of the contrast medium, although this can increase during storage. Once administered, more free iodine may be released as a result of the activity of the de-iodizing enzymes in the mother's or the child's body. The effect of free iodide on the infant's thyroid depends on the iodine saturation before the study began. It there is a latent deficiency status, flooding with iodine is more likely to lead to an effect on function than it would if the iodine supply were well adjusted.
The implication ol the iodine transfer to the baby, following an examination of the breastfeeding mother using a contrast agent, cannot be adequately determined simply by measuring the iodine in the infant's urine. It is only with an examination of the infant's iodine uptake and thyroid function that the individual situation can be described precisely.
In cases of direct use of iodine-containing contrast media, particularly in infants under 3 months of age, transient hypothyroidism has been described. There are no known cases of gross impairment to breastfed infants following administration to the mother. However, discrete effects on the sensitive central nervous system differentiation in infancy cannot be ruled out when there has been maternal exposure with subsequent iodine transfer via breast milk.
In the case of iohexol and metrizoate, Nielsen and colleagues concluded that a noteworthy exposure which would be a barrier to breastfeeding should not be expected (Nielsen 1987). However, this seems questionable, since one of the four subjects in his study, with ongoing high iodine concentrations of up to 141 mg/l milk, was not considered when his study results were summarized. The authors calculated half-lives in the milk of 15-108 hours for iohexol and metrizoate. In the scrum, by contrast, the half-lives of the water-soluble contrast media are, at 2 hours, considerably shorter.
In the case of the fat-soluble iopanoic acid used for biliary duct examination, 7% of the maternal weight-related dosage was calculated for the breastfed infant in an older study (Holmdahl 1956).
There is no published experience on the other iodine-containing contrast media, such as iobitridol, iodixanol, iomeprol, iopamidol, iopentol, iopodate, iopromide, iotalaminic acid, iotrolan, iotroxine acid, ioversol, ioxagtinic acid, ioxitalaminic acid, lysine amido-tri-zoate. and sodium iodine (with and without indocyanin green).
Recommendation. When a mother is given an iodine-containing contrast agent, the possibility that the infant will absorb a significantly higher quantity of free iodide than would be necessary for supplementation cannot be ruled out (see Chapter 4.11). The need for such an examination should be very critically considered. With the extensive choice of other procedures, such as ultrasound, computer tomography, and magnetic resonance imaging, there are safer options. If the use of an iodine-containing contrast agent is unavoidable, breastfeeding should be interrupted for 24-48 hours, at least for the young, fully breastfed infant. This period can be bridged with milk that has been pumped ahead of time.
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