Mutational resistance to 4-quinolone antibacterial agents.

The activity of ten 4-quinolone drugs was tested against five Escherichia coli mutants. Mutational resistance was found to reduce the activity of all ten drugs, indicating that they display biochemical cross-resistance with each other. However, ciprofloxacin and, to a lesser extent, ofloxacin and norfloxacin were so highly active that the most resistance exhibited by any mutant fell well within the serum drug concentration ranges attainable in humans. Hence, clinical cross-resistance in Escherichia coli at least, need not necessarily apply to such highly active 4-quinolone antibacterial agents.