The relative potencies of the fluoroquinolones can be assessed according to pharmacodynamic factors. Could you comment on this?
Potency is a term that has gained increasing prominence over the last few years. In the past, antibiotic potency tended to be measured in a very simple manner according to minimum inhibitory concentrations (MICs) attained against respective pathogens. However, it is now clearly recognized that measuring potency is much more complicated than this, and requires assessment of the important relationship between drug exposure and MIC. While MIC values solely reflect in vitro potency, the more clinically relevant in vivo potency is reflected in the relationship between the MIC and the pharmacokinetic/pharmacodynamic (PK/PD) features of an agent. Therefore, the potency of a fluoroquinolone is determined by the peak serum/tissue levels achieved (Cmax) and the area under the concentration-time curve (AUC) and the ratio of these factors to the MIC. Previous research evaluating dose-response curves for fluoroquinolones has demonstrated that the clinical cure rate can rise above 90% when the AUC/MIC ratio ranges from 30 to 35 for Streptococcus pneumoniae and between 100-125 for Gram-negative pathogens (Figure 2) (3-5).
In vitro activity does not necessarily correlate with clinical results.
Abbreviations: S. pneumoniae = Streptococcus pneumoniae , AUC = area under the plasma concentration-time curve, MIC = minimum inhibitory concentration.
Adapted from reference (4-7).