Entex has been discussed on Lactnet previously.  It is an
expectorant/decongestant.
There is no problem for the nursing infant.  There is a slight chance of
decreased milk volume.  The mother should drink extra fluids (or chicken soup!)
while taking an expectorant/decongestant anyway for her own benefit.
Frank J. Nice, DPA, CPHP
In Bethesda, MD at this exact moment