MICROBIOLOGY Levofloxacin is the L-isomer of the racemate, ofloxacin, a quinolone antimicrobial agent. The antibacterial activity of ofloxacin resides primarily in the L-isomer. The mechanism of action of levofloxacin and other fluoroquinolone antimicrobials involves inhibition of bacterial topoisomerase IV and DNA gyrase (both of which are type II topoisomerases), enzymes required for DNA replication, transcription, repair and recombination. Levofloxacin has in vitro activity against a wide range of gram-negative and gram-positive microorganisms. Levofloxacin is often bactericidal at concentrations equal to or slightly greater than inhibitory concentrations. Fluoroquinolones, including levofloxacin, differ in chemical structure and mode of action from aminoglycosides, macrolides and -lactam antibi-otics, including penicillins. Fluoroquinolones may, therefore, be active against bacteria resistant to these antimicrobials. Resistance to levofloxacin due to spontaneous mutation in vitro is a rare occurrence (range: 10 -9 to 10 -10 ). Although cross-resistance has been observed between levofloxacin and some other fluoroquinolones, some microorganisms resistant to other fluoroquinolones may be susceptible to levofloxacin. Levofloxacin has been shown to be active against most strains of the following microorganisms both in vitro and in clinical infections as described in the INDICATIONS AND USAGE section: Aerobic gram-positive microorganisms Enterococcus faecalis (many strains are only moderately susceptible) Staphylococcus aureus (methicillin-susceptible strains) Staphylococcus epidermidis (methicillin-susceptible strains) Staphylococcus saprophyticus Streptococcus pneumoniae (including penicillin-resistant strains*) Streptococcus pyogenes *Note: penicillin-resistant S. pneumoniae are those strains with a penicillin MIC value of 2 µg/ mL | ||||
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