The in vivo antichlamydial activities of
sparfloxacin and reference drugs were examined in a experimental model of
pneumonia caused by Chlamydia pneumoniae in leukopenic mice; their in vitro activities were also examined. The most potent agents in vitro were
sparfloxacin (MICs for C. pneumoniae Kajaani and IOL 207, (0.031 and 0.031 micrograms/ml, respectively),
clarithromycin (0.031 and 0.031 micrograms/ml, respectively), and
minocycline (0.031 and 0.031 micrograms/ml, respectively); these were followed by
tosufloxacin (0.063 and 0.125 micrograms/ml, respectively) and
ofloxacin (0.5 and 0.5 micrograms/ml, respectively). The MBCs of
sparfloxacin,
tosufloxacin,
ofloxacin,
clarithromycin, and
minocycline for these two strains were 0.063 and 0.063 micrograms/ml, 0.125 and 0.25 micrograms/ml, 1.0 and 1.0 micrograms/ml, 0.125 and 0.125 micrograms/ml, and 0.25 and 0.25 micrograms/ml, respectively. Fatal
pneumonia was induced by intranasal inoculation of
cyclophosphamide-treated leukopenic mice with C. pneumoniae IOL 207; infiltration of neutrophils and lymphocytes was observed in the lungs of these mice by histopathological examination. The 50% effective dose of
sparfloxacin (oral dose of 0.97 mg/kg of
body weight) against the
pneumonia was the lowest among the drugs tested; this was followed by those of
minocycline (2.22 mg/kg),
tosufloxacin (3.47 mg/kg),
clarithromycin (4.66 mg/kg), and
ofloxacin (16.6 mg/kg). The results indicate that it may be worthwhile to use
sparfloxacin against C. pneumoniae
infections in humans.