Therapeutic options in an era of decreasing antimicrobial susceptibility.

Antimicrobial resistance among human pathogens has evolved to the multidrug-resistant phase. Consequently, preserving antimicrobial efficacy is now an important clinical consideration when selecting an agent for therapy. A new, in vitro measure of potency called the mutant prevention concentration (MPC) allows clinicians to select antibacterials on the basis of an agent's ability to restrict the selection of resistant mutants. With some pathogens, C-8-methoxy fluoroquinolones are expected to be quite effective at restricting the selection of resistance because the value of MPC is below the human serum drug concentration achieved with standard doses. Clinical trials are now needed to determine how well preclinical profiles of these drugs correlate with the prevention of resistance.