Activity of trovafloxacin (with or without ampicillin-sulbactam) against enterococci in an in vitro dynamic model of infection.
Antibiotic-resistant enterococci are being increasingly identified as causal agents of infection. Trovafloxacin is a new fluoronaphthyridone with enhanced activity against gram-positive cocci and variable activity reported against Enterococcus spp. Twenty-one strains of vancomycin-resistant Enterococcus faecium and two strains of Enterococcus faecalis (one vancomycin resistant) were studied at an initial inoculum of 10(6) CFU/ml in time-kill assays with trovafloxacin (3 mg/liter), ampicillin-sulbactam (100/50 mg/liter), and the combination. Six strains of E. faecium (five vancomycin resistant) also were studied in an in vitro two-compartment dynamic model that mimics human pharmacokinetics with trovafloxacin simulated at 300 mg every 12 h (q12h), ampicillin-sulbactam at 2/1 g q6h, and the combination. Peripheral compartments were sampled q2h for 30 h for bacterial counts. Trovafloxacin MICs ranged from 0.5 to 32 mg/liter, and the nine strains of vancomycin-resistant E. faecium for which MICs were < or =2 mg/liter were more likely to show a reduction of 2 log units or more in viable counts in time-kill assays than were strains for which MICs were higher. Synergism with ampicillin-sulbactam was found for only one strain (trovafloxacin MIC, 16 mg/liter). Similar results were obtained in the pharmacokinetic model, with 2- to 4-log-unit reductions in viable bacteria for trovafloxacin-susceptible strains. Although no convincing evidence of synergism was found, ampicillin-sulbactam in combination minimized late bacterial regrowth of two trovafloxacin-susceptible strains. These data suggest that this high dose of trovafloxacin (with or without ampicillin-sulbactam) might be useful against strains of vancomycin-resistant E. faecium for which MICs were < or =2 mg/liter.
Zinner
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SH
Department of Medicine, Brown University, Roger Williams Medical Center, Providence, Rhode Island 02908, USA. Stephen.Zinner@brown.edu
Gilbert
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D
Dudley
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MN
D000667:Ampicillin / Q000494:pharmacology; D000890:Anti-Infective Agents / Q000494:pharmacology*; D004352:Drug Resistance, Microbial; D004357:Drug Synergism; D004359:Drug Therapy, Combination / Q000494:pharmacology*; D013293:Enterococcus faecalis / Q000187:drug effects*; D016984:Enterococcus faecium / Q000187:drug effects*; D024841:Fluoroquinolones; D016908:Gram-Positive Bacterial Infections / Q000188:drug therapy*; D008826:Microbial Sensitivity Tests; D009287:Naphthyridines / Q000494:pharmacology*; D013407:Sulbactam / Q000494:pharmacology
D000890:Anti-Infective Agents; D024841:Fluoroquinolones; D009287:Naphthyridines; C035444:sultamicillin; D000667:Ampicillin; C080163:trovafloxacin; D013407:Sulbactam