Stan Brown wrote:

Good lord. Let me reassure you: antibiotics do *not* "go right
through you". Maybe you're thinking of the sometime side effect of
diarrhea -- that happens when antibiotics kill the digestion-aiding
bacteria in your gut along with the ones that are making you sick.


No. This link refers to animals, but the effect is similar in humans:

Antibiotics are routinely used in livestock production as both a prophylactic
and growth promoter. Due to low absorption rates, it has been estimated that as
much as 75% of antibiotics administered to feedlot animals could be excreted
unaltered in feces.

http://www.seas.harvard.edu/envmicro/research.html

Antibiotics must be taken for the full course because when your
symptoms disappear a few of the bad bacteria are still living. These
are the ones that have lower susceptibility to the antibiotic. You
continue taking the medicine to kill those. Otherwise they quickly
breed back to high numbers and make you sick again, but this time you
have a strain that is resistant to the antibiotic.

That's true, but the course is based on the bioavailability of the drug, which
is a small percentage of the size of the dose. That's why many drugs state "do
not crush", or restrict what foods you can use. Milk in particular can lower the
amount of drug that gets absorbed by the body.

--
"Tell me what I should do, Annie."
"Stay. Here. Forever." - Life On Mars