I would guess this is clonazepam (Rivotril in Canada).  It is a
benzodiazepine with a long half life.  Nevertheless serum blood levels
are very low with this drug with the baby likely to get no more than a
few micrograms in a day.  If it's so dangerous, why is it okay for the
baby to be exposed to this drug in utero?

The risks of breastfeeding I think would be far outweighed by the
risks of not breastfeeding.  Indeed, with this group of drugs, the
risk of withdrawal is possible and might be mitigated by the mother's
breastfeeding.

This drug is used in large doses in newborns with seizures.

Jack Newman, MD, FRCPC