Protective effect of trovafloxacin, ciprofloxacin and ampicillin against Streptococcus pneumoniae in a murine sepsis model

Trovafloxacin is a new fluoroquinolone that has potent microbiological acti vity against the pneumococcus, including penicillin-resistant strains. To e valuate the protective effect of trovafloxacin, ciprofloxacin and ampicilli n against penicillin-susceptible, -intermediate and -resistant strains of S treptococcus pneumoniae, an intraperitoneal, immunocompetent mouse model of sepsis was used. The minimum lethal dose (MLD) for each isolate was determ ined in duplicate. A single sc dose of each antibiotic was administered ove r a wide range of doses 1 h after the ip inoculation of the test isolate at the MLD. The assessment of the protective dose for 50% of the population ( PD50) for each antimicrobial/bacteria combination was performed in triplica te and the PD50 value was calculated at the end of 5 days. Results showed t hat trovafloxacin provided PD50 values that were significantly lower than t hose of ciprofloxacin for all isolates. For the penicillin-susceptible and -intermediate isolates, the PD50 values of ampicillin were significantly lo wer than those for either of the fluoroquinolones studied; however, trovafl oxacin was statistically superior to both ciprofloxacin and ampicillin agai nst the penicillin-resistant strain. Therefore, regardless of penicillin su sceptibility, trovafloxacin has potent activity against Streptococcus pneum oniae and may be a viable alternative for the treatment of penicillin-resis tant isolates.