Predicting an antibiotic’s activity from standard in vitro MICs alone is insufficient to predict in vivo potency. It is also necessary to consider serum and tissue concentrations as well as pharmacokinetic characteristics. In regard to the fluoroquinolones, the area under the inhibitory curve (or AUIC) and peak concentration/MIC ratio predict clinical cure. Results from clinical trials and animal models indicate that a peak/MIC ratio of 10/1 and above and an AUIC of 125 and above are predictive of a clinical cure for fluoroquinolones against Gram-negative pathogens and an AUIC greater than 30 predicts efficacy against Gram-positives.