title: Activity of gatifloxacin in an in vitro pharmacokinetic-pharmacodynamic model against Staphylococcus aureus strains either susceptible to ciprofloxacin or exhibiting various levels and mechanisms of ciprofloxacin resistance.
abstract: Gatifloxacin (GAT) is a new 8-methoxy fluoroquinolone with enhanced activity against gram-positive cocci. Its activity was studied in an in vitro pharmacokinetic-pharmacodynamic model against five Staphylococcus aureus strains, either susceptible to ciprofloxacin or exhibiting various levels and mechanisms of ciprofloxacin (CIP) resistance: the ATCC 25923 reference strain (MICs of CIP and GAT: 0.5 and 0.1 microg/ml, respectively), its efflux mutant SA-1 (16 and 0.5 microg/ml; mutation in the norA promoter region), and three clinical strains, Sa2102 (2 and 0.2 microg/ml), Sa2667 (4 and 0.5 microg/ml), and Sa2669 (16 and 1 microg/ml), carrying mutations in the grlA (Ser80Tyr or Phe) and gyrA (Ser84Ala) quinolone resistance-determining regions (QRDRs) for Sa2669. Plasmatic pharmacokinetic profiles after daily 1-h perfusion of 400 mg for 48 h were accurately simulated. Thus, mean maximum concentration of drug in serum values for the two administration intervals were 5.36 and 5.80 microg/ml, respectively, and the corresponding half-life at beta-phase values were 8.68 and 7.80 h (goodness of fit coefficient, >0.98). Therapeutic concentrations of GAT allowed the complete eradication of the susceptible strain within 12 h (difference between the bacterial counts at the beginning of the treatment and at a defined time: -2.18 at the 1-h time point [t(1)] and -6.80 at t(24) and t(48); the bacterial killing and regrowth curve from 0 to 48 h was 30.2 h x log CFU/milliliter). However, mutants (M) with GAT MICs increased by 4- to 40-fold were selected from the other strains. They acquired mutations either supplementary (MSa2102 and MSa2667) or different (Ala84Val for MSa2669) in gyrA or in both gyrA and grlA QRDRs (MSA-1). MSa2667 additionally overproduced efflux system(s) without norA promoter modification. Thus, GAT properties should allow the total elimination of ciprofloxacin-susceptible S. aureus, but resistant mutants might emerge from strains showing reduced susceptibility to older fluoroquinolones independently of the first-step mutation(s).
authors.affiliation: Laboratoire de Pharmacocinétique et de Pharmacie Clinique, EA525, Faculté de Pharmacie, Université Victor Segalen Bordeaux 2, France. boubakar.ba@phcocin.u-bordeaux2.fr
authors.forename: Boubakar B
authors.initials: BB
authors.lastname: Ba
authors.forename: Corinne
authors.initials: C
authors.lastname: Arpin
authors.forename: Céline
authors.initials: C
authors.lastname: Vidaillac
authors.forename: Arnaud
authors.initials: A
authors.lastname: Chausse
authors.forename: Marie-Claude
authors.initials: MC
authors.lastname: Saux
authors.forename: Claudine
authors.initials: C
authors.lastname: Quentin
mesh_terms: D000890:Anti-Infective Agents / Q000494:pharmacology*; D019540:Area Under Curve; D002939:Ciprofloxacin / Q000494:pharmacology*; D003198:Computer Simulation; D024881:Drug Resistance, Bacterial / Q000235:genetics; D024841:Fluoroquinolones / Q000493:pharmacokinetics* / Q000494:pharmacology*; D000077734:Gatifloxacin; D006207:Half-Life; D066298:In Vitro Techniques; D008826:Microbial Sensitivity Tests; D009154:Mutation; D012015:Reference Standards; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification
chemical_list: D000890:Anti-Infective Agents; D024841:Fluoroquinolones; D002939:Ciprofloxacin; D000077734:Gatifloxacin