SECRETION OF RADIOACTIVITY IN BREAST-MILK FOLLOWING ADMINISTRATION OF TC-99M-MAG3

Measurements were made of the fraction of injected radioactivity which was secreted in breast milk following Tc-99(m)-MAG3 dynamic renal scans of two nursing mothers. The activity concentration in the milk expressed at different times after injection was found to decrease monoexponentially, with effective half-lives of 3.2 and 4.0 h. Two models were applied to each set of data and predicted an overall mean infant effective dose equivalent per unit administered activity of 2.9 muSv MBq-1 and a maximum of 4.5 muSv MBq-1. The results demonstrated that it was not essential to interrupt breast feeding following administration of 100 MBq Tc-99(m)-MAG3 for a dynamic renal scan. If a renal perfusion scan is performed using greater activities of Tc-99(m)-MAG3, the mother should interrupt feeding and not resume until measurements on her expressed milk samples indicate that the effective dose equivalent to the infant will be less than 1 mSv. However, it was noted that a considerably lower radiation dose to the infant could be achieved by using Tc-99(m)-DTPA. Therefore, it was concluded that whenever clinically appropriate Tc-99(m)-DTPA should be used for both types of renal investigations of breast-feeding mothers.