The antibacterial effects of ciprofloxacin and trovafloxacin against Streptococcus pneumoniae in an in vitro dynamic model

Objective: To determine whether the newer fluoroquinolone antibiotics such as trovafloxacin posses enhanced activity against Gram-positive organisms, including Streptococcus pneumoniae, because the clinical activity of older quinolones against pneumococci has been questioned. Methods: In this study, the bactericidal activities of ciprofloxacin and trovafloxacin against six strains of penicillin-resistant and -sensitive strains of Streptococcus pneumoniae were compared using an in vitro model that simulates human pharmacokinetics. Ciprofloxacin was administered at 750 mg every 12 h, higher than the usual daily dose of 500 mg twice a day. Trovafloxacin was administered at 300 mg every 24 h for the six strains and at 200 mg every 24 h for three of the strains. Results: The single 300-mg dose of trovafloxacin killed five of the six strains in 4 h, with no bacterial regrowth. Ciprofloxacin reduced the initial inoculum by 3-5 logs by 24 h. Although the 300-mg dose of trovafloxacin more rapidly eradicated susceptible strains, the activity of trovafloxacin at 200 mg every 24 h was similar to that of ciprofloxacin at 750 mg every 12 h against the three strains tested. Conclusion: Trovafloxacin (and ciprofloxacin at high doses) eradicates susceptible strains of pneumococci in an in vitro dynamic model.