You don't excrete antibodies? I think you might be saying that antibiotics are passive strategies which are inherently overly broad and thus problematic.
To give you an idea of the weight difference, an average human IgG[1] antibody is about 500 more massive than a pretty average small molecule antibiotic like levofloxacin[2]
Their fate mostly lies in catabolism, i.e. they are broken down and the components reused. Biliary excretion accounts for a very small amount of the elimination of IgG antibodies.
[0] "Pharmacokinetics of Monoclonal Antibodies" http://onlinelibrary.wiley.com/doi/10.1002/psp4.12224/pdf
I tried adding this quote from the linked paper:
> Thus, IgG elimination occurs mostly through intracellular catabolism by lysosomal degradation to amino acids after uptake by either pinocytosis, an unspecific fluid phase endocytosis, or by a receptor-mediated endocytosis process.
Explanation of two words in there that maybe not everybody knows:
pinocytosis: The ingestion of liquid into a cell by the budding of small vesicles from the cell membrane.
endocytosis: The taking in of matter by a living cell by invagination of its membrane to form a vacuole.
EDIT: I can still edit this comment more than five minutes later, as expected. Hmm... why could I not do that with my first comment...?
I missed it when I wrote my reply, concentrating on the immediate question (interesting psychological problem) - and then I could not edit it. It bothered me quite a bit but I did not want to write a third reply. Interesting to see how easy it is to get sidetracked on an irrelevant (albeit interesting) question, and how hard it is to get the discussion back on track.