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.

ke 为肠道环丙沙星（ciprofloxacin）浓度的消除速率常数；gS与gR分别为源自外界的敏感型与耐药型细菌的恒定来源；kT 为未接受治疗时肠杆菌（enterobacteria）的清除速率常数；δmax 为环丙沙星对肠杆菌的最大杀灭速率；C50S与C50R分别为敏感型、耐药型肠杆菌达到50%最大杀灭效应时对应的环丙沙星浓度。