Model used for the kinetics of susceptible (S) and resistant (R) enterobacteria in presence of ciprofloxacin (C) in intestinal flora.

ke is the elimination rate constant of intestinal ciprofloxacin concentrations; gS and gR are constant sources of susceptible and resistant bacteria respectively coming from outside; kT is the rate constant of enterobacteria loss in absence of treatment; δmax is the maximal killing rate of enterobacteria by ciprofloxacin; C50S and C50R are the ciprofloxacin concentrations at which 50% of the maximal killing effect occurs in susceptible and resistant enterobacteria respectively.