Medication in expressed breast milk eventually breaks down and loses
potency; some faster than others and some more slowly than others.  The FDA
and drug manufacturer would have potency data for drugs in solution or
suspension, but not necessarily in breast milk, but it should be somewhat
similar.  Drugs like tetracycline would become nonpotent because of binding
with calcium in milk.  So there are as many answers to this question as
there are drugs.  Generalities can be made though.
Eventually all medications "dissipate" eventually, especially when in
solution.
This is the first that I have heard that Demerol is "incompatible with
breastfeeding."
Yes, it could be frozen with probably little degradation in potency of the
Demerol.  It should still be present in milk, unless freezing destroys the
Demerol molecule, which I do not know if it does or not.  Once again, only
the drug manufacturer or the FDA knows.  I do know there are warnings on
freezing medications, but that may have more to do with the consistency of
the vehicles that the medications are in.
Hope this helps.
Frank J. Nice, DPA, CPHP

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