When in doubt, especially for one dose, assume it's okay.  The amount
of magnesium the mother will absorb is fairly minimal.  It is not
going to raise her blood levels significantly and the baby will not be
affected.

Too late for this patient, but in future.

"When in doubt, the *conservative* approach is to continue
breastfeeding"  Newman, 1984, 85, 86, 87, 88, 89, 90,...

Jack Newman, MD, FRCPC