Yes, you are correct.  But you also have to take into consideration that
*not breastfeeding* is also associated with risks.  Some well demonstrated,
others not.  The question then comes to: which is riskier, breastmilk with a
tiny amount of drug in it, or a drug (formula) with no breastmilk in it?

Breastfeeding is too important to sacrifice because the health provider
can't be bothered to check if a drug is contraindicated or not.  And because
s/he can't really make himself believe that breastfeeding is better.  And,
truthfully, I don't believe that many do it from altruistic motives.  They
just assume that breastmilk and formula are the same, and thus breastmilk
with cloxacillin in it is riskier than formula.  This is ignorance, not
altruism.  And let us not forget that many, too many, worry about, shh! not
too loudly, the medical legal aspect of telling mothers it's alright to
continue breastfeeding.

I remember a communication I had with the chief of radiology of a hospital
here in Toronto regarding a mother who was told she had to stop
breastfeeding for 24 hours because she was going to have an IVP.  I
mentioned all the point I usually do.  And he wrote back to tell me that
everything I said was true, but because it says in the package insert that
lactating women should be advise to interrupt breastfeeding for 24 hours, he
could not risk telling them otherwise.

Jack Newman, MD, FRCPC