Maximizing efficacy and reducing the emergence of resistance

An understanding of the pharmacokinetic and pharmacodynamic properties of antimicrobial agents enables better choices to be made in the clinical situation. The fluoroquinolones share several useful pharmacokinetic properties, such as good bioavailability (in most cases >85%) and the ability to penetrate and concentrate intracellularly, giving them activity against pathogens such as Legionella pneumophila and Listeria monocytogenes. Nevertheless, there are some important differences between the fluoroquinolones, and even the newer fluoroquinolones demonstrate a range of pharmacodynamic properties. When considering the area under the inhibition curve (AUIC) and the Cmax/MIC, the comparative figures are: ciprofloxacin and ofloxacin (5-25, 1-5); levofloxacin, grepafloxacin and gatifloxacin (25-75, 5-10); trovafloxacin (75-250, 10-20) and moxifloxacin, clinafloxacin and gemifloxacin (>250, >20). The development of resistance is also a concern, and selecting an agent that reaches an adequate concentration above the MIC will reduce the opportunity for resistance to develop. These properties should be considered when selecting a fluoroquinolone either for inclusion in a formulary, or for use in an individual patient.