Aim for Cmax:MIC ratio of 10-12.
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:
- total vs free drug concentration (takes into account protein binding)
- bacteriostatic vs bactericidal activity
- Gram positive or Gram negative (higher AUC24/MIC ratio generally required for Gram negative infections)
- inoculum at site of infection
- immune status of the host (higher AUC24/MIC ratio required in immuno-compromised patients).