As concentration-dependent antibacterials, the efficacy of fluoroquinolones has been shown to correlate with the ratio of the peak serum concentration to the MIC of the organism (Cmax:MIC), as well as the ratio of the 24 hour area under the plasma concentration curve (AUC24:MIC). Optimizing the AUC24:MIC ratio can result in better clinical outcomes and limit the development of resistance.  Various AUC24:MIC target ratios have been proposed in the literature but no firm recommendations can be made as these ratios are dependent on multiple factors including:

- antibiotic

  • total vs free drug concentration (takes into account protein binding)
  • bacteriostatic vs bactericidal activity

- organism

  • Gram positive or Gram negative (higher AUC24:MIC ratio generally required for Gram negative infections)
  • MIC
  • inoculum at site of infection

- immune status of the host (higher AUC24:MIC ratio required in immuno-compromised patients).