Human breast milk excretion of iodine-131 following diagnostic and therapeutic administration to a lactating patient with Graves' disease.

Previous reports on the excretion of 131I into human breast milk have recommended discontinuance of breast feeding from 1 to 12 days following diagnostic tracer doses of 131I. Recent excretion models have calculated that breast feeding could safely resume 56 days following a 5 microCi (0.185 MBq) 131I maternal tracer dose. We studied a postpartum patient with Graves' disease following first an uptake dose of 8.6 microCi (0.317 MBq) and then for 38 days following a 9.6 mCi (355 MBq) therapy dose of Na131I. We calculated from our data that although nursing could not be safely resumed for 46 days following the 8.6-microCi uptake dose, nursing could resume in this patient 8 days after a 100-nCi (3.7 KBq) dose. Extrapolating this data to impure 123I (p, 2n or p, 5n) we feel that standard 100-microCi (3.7 MBq) doses of either 123I preparation is not suitable if nursing is to be resumed.