In vitro activity: Levofloxacin is active against most aerobic Gram-positive and Gram-negative organisms and demonstrates moderate activity against anaerobes. Levofloxacin is two-fold more active than ciprofloxacin against Streptococcus pneumoniae and 2- to 4-fold more active than ciprofloxacin against Staphylococcus aureus, Xanthomonas maltophilia, and Bacteroides fragilis. Levofloxacin is two- to eightfold more active than ciprofloxacin against coagulase-negative staphylococci and Acinetobacter spp., although these improvements in potency may not be clinically relevant. Levofloxacin inhibits 90% of streptococci when it is used at concentrations of 1 mg/mL to 2 mg/mL. Levofloxacin exhibits twofold greater inhibitory and bactericidal activities than ofloxacin against either extracellular or intracellular tubercle bacilli. Levofloxacin has the least inhibitory effect on osteoblastic cell growth, with a 50% inhibitory concentration of approximately 80 mg/mL at 48 and 72 hours. Levofloxacin results in strong inhibition of calcium deposition, as determined on day 14 by alizarin red staining and biochemical analysis. Levofloxacin inhibits glycosaminoglycan synthesis initially and DNA synthesis and mitochondrial function secondarily at actual arthropathic concentrations in cultured rabbit chondrocytes but that these changes are reversible and not enough to kill the cells.

Drugs. 1994 Apr;47(4):677-700; Antimicrob Agents Chemother. 1992 Apr;36(4):860-6.