The activities of
levofloxacin and
ofloxacin against 22 clinical legionella isolates was determined by microbroth dilution susceptibility testing. Growth inhibition of two Legionella pneumophila strains grown in guinea pig alveolar macrophages by
levofloxacin,
ofloxacin, or
erythromycin was also determined. The
drug concentrations required to inhibit 90% of strains tested was 0.032 mg/L for
levofloxacin or
ofloxacin, and was 0.016 mg/L for
ciprofloxacin. BYE alpha broth significantly inhibited the activities of all three drugs tested, as judged by the susceptibility of control Escherichia coli strains.
Levofloxacin (0.25 mg/L) reduced bacterial counts of two L. pneumophila strains grown in guinea pig alveolar macrophages by 1 log10, but regrowth occurred over a 3 day period;
levofloxacin (1 mg/L) reduced bacterial counts by 2-3 log10 cfu/mL.
Levofloxacin was significantly more active than
erythromycin, and as active as
ofloxacin or
ciprofloxacin in this assay. Pharmacokinetic and
therapy studies of
levofloxacin and
ofloxacin were performed in guinea pigs with L. pneumophila
pneumonia. For the pharmacokinetic study,
levofloxacin was given (10 mg/kg) by the intraperitoneal route to infected guinea pigs; mean peak plasma and lung concentrations were 3.4 mg/L and 1.4 micrograms/g, respectively, at 0.5 h and 2.6 mg/L and 0.6 micrograms/g at 1 h. The terminal half-life phase of elimination from plasma and lung was c. 1 h. All 15 infected guinea pigs treated with
levofloxacin (10 mg/kg/day given ip once daily) for 5 days survived for 9 days after antimicrobial
therapy, as did all 14 guinea pigs treated with the same dose of
ofloxacin. None of 13 animals treated with saline survived.
Levofloxacin is effective against L. pneumophila in vitro and in a guinea pig model of
legionnaire's disease.
Levofloxacin should be evaluated as a treatment of human
legionnaires' disease.