The future of fluoroquinolones.

The mutant prevention concentration (MPC) is a new measure of antibiotic potency above which a microbe must attain two concurrent resistance mutations for growth. For some C-8-methoxy fluoroquinolone-pathogen combinations, the value of MPC is below human serum drug concentration achieved with standard doses. Although untested clinically, such a low value of MPC, coupled with high serum concentration, should allow these fluoroquinolones to restrict severely the selection of resistant mutants when used as monotherapy. Compounds that cannot meet the MPC-pharmacokinetic criterion will enrich resistant mutants unless they are a part of combination therapy. Separation of fluoroquinolones into groups suitable for monotherapy or for combination therapy, followed by appropriate adminstration, may help extend the lifespan of the fluoroquinolones.