Sorry, Andrew, but I think you got it wrong.  There is no evidence of
ciprofloxacin causing arthropathies in humans.  See reference:

Scaad UB. Role of the quinolones in pedaitric practice. Pediatr Infect Dis J
1992;11:1043-6.

The author followed children with cystic fibrosis treated for years, some of
them with ciprofloxacin, and found no evidence of arthropathy.  They were
followed with MRI or, if they died, at autopsy.

Furthermore, what the mother gets is *not* what the baby gets.  As a rule of
thumb, 1% of the maternal dose is what the baby gets in the milk.  If you
look in Hale's book, however, you can see that in at least one study
(admittedly of one nursing couple), the dose to the baby was much less than
1%, more like about 0.2% of the maternal dose.  For a more common drug, 1%
of 1500 mg of amoxycillin (a typical adult dose) is 15 mg, much less than we
would give even a 4 kg baby, and not enough to worry one E. coli, I would
say.

Jack Newman, MD, FRCPC