Levofloxacin In Vitro Activity: Results from an International Comparative Study with Ofloxacin and Ciprofloxacin

Summary

Levofloxacin, the S-(-)-isomer of ofloxacin, was compared to ofloxacin and ciprofloxacin against <6000 recent clinical isolates of Gram-positive and Gram-negative bacteria from six different countries. This international multicenter study demonstrated a high level of antibacterial activity of levofloxacin against all the members of Enterobacteriaceae [minimum inhibitory concentration (MIC)₅₀s, ≤0.03 to 0.12 mg/L] except Providencia rettgeri (MIC₅₀, 2 mg/L), and Providencia stuartii (MIC₅₀, 1 mg/L). Oxacillin-susceptible staphylococci (MIC₅₀S, 0.12 to 0.25 mg/L), enterococci (MIC₅₀s, 0.5 to 2 mg/L), and streptococci (MIC₅₀s, 0.5 mg/L) were also susceptible to levofloxacin, but most isolates of oxacillin-resistant staphylococci had MICs of ≥4 mg/L. Levofloxacin was also active against non-enteric Gram-negative bacilli, including Acinetobacter species (MIC₅₀s, ≤0.03 to 1 mg/L), Pseudo-monas species (MIC₅₀s, 0.5 to 1 mg/L) and Xanthomonas maltophilia (MIC₅₀, 0.5 mg/L). Overall, levofloxacin inhibited 50% and 90% of all the tested strains at the concentrations of 0.12 and 4 mg/L, respectively. The activity of levofloxacin was generally two-fold greater than ofloxacin and equal to or slightly less potent than ciprofloxacin.

Key Words:

• levofloxacin
• fluoroquinolone
• antimicrobial susceptibility
• international multicenter trial.