Ciprofloxacin, a new carboxyquinolone, has potent in vitro bactericidal activity against the major aerobic, gram-negative bacillary pathogens that cause human pyoarthroses. We investigated the in vivo efficacy of
ciprofloxacin in a rabbit model of
septic arthritis due to Escherichia coli. Animals received either
ciprofloxacin (80 mg/kg per day) or
gentamicin (5 mg/kg per day).
Ciprofloxacin was rapidly bactericidal in vivo and was significantly more effective in reducing the numbers of E. coli in synovial tissue than was
gentamicin at days 10 and 17 of
therapy (P less than .0005 and P less than .05, respectively). Similarly,
ciprofloxacin was significantly more active than was
gentamicin in reducing the numbers of E. coli in joint fluid on day 10 of
therapy (P less than .0005); however, by day 17 of
therapy, the numbers of E. coli in joint fluid were not significantly different in the two
therapy groups. Neither regimen was effective in preventing the development of postinfectious inflammatory
synovitis. There was no in vivo development of resistance to either
antibiotic during
therapy.
Ciprofloxacin therapy was associated with significantly higher bactericidal titers in serum and joint fluid than were observed with
gentamicin therapy (P less than .0005).
Ciprofloxacin warrants further in vivo evaluation in invasive E. coli
infections.