Japanese demonstrate the excellent efficacy of levofloxacin against S. pneumoniae
Streptococcus pneumoniae is a very common pathogen found in adult patients with community-acquired pneumonia. In Japan, high-dose penicillin therapy is often given empirically to treat adults with such a condition, and proactive use of respiratory quinolones is encouraged for the treatment of the elderly and patients with underlying respiratory conditions. This study carried out by Japanese researchers, describes the bactericidal activity of this formulation and other antibiotics in a strain of S. pneumoniae, ATCC 49619 since 2011 saw the launch of Cravit Intravenous Drip Infusion (an injectable form of levofloxacin) in Japan.
The in vitro bactericidal activity of levofloxacin was measured at a concentration equivalent to the peak plasma concentration (Cmax) after administration of Cravit Intravenous Drip Infusion 500mg in the stationary phase which is regarded as reflecting the condition of the pathogen at the site of infection. It is also accepted that the bactericidal activity of antimicrobial agents against bacteria in the stationary phase correlates closely with the therapeutic efficacy of these agents in in vivo models of chronic infection and this also reflects the efficacy in clinical situations.
The MIC values of the antibiotics were measured using the agar gel diffusion method. When the test strain of S. pneumoniae in the stationary phase was exposed to levofloxacin at a concentration corresponding to the Cmax in humans, it exhibited bactericidal activity after 3 hours of exposure and the viable cell count fell below the limit of detection after an exposure of 4 hours. When the S. pneumoniae strain in the log phase was exposed to levofloxacin at the same concentration, the viable cell count fell below the limit of detection after 3 hours of exposure.
These findings suggest that levofloxacin exhibits potent bactericidal activity against S. pneumoniae regardless of the growth cycle of the organism. When a comparison was carried out using ceftriaxone and sulbactam/ampicillin at concentrations corresponding to their respective Cmax values achieved with the standard dose in humans, none of these antibiotics exhibited any bactericidal activity.
The results of this detailed study show that, although penicillins and cephems produce bacteriostatic activity, only levofloxacin was able to produce bactericidal activity against S. pneumoniae in the stationary phase which is regarded as the state of the bacteria at the site of infection when each drug was present at a concentration corresponding to the Cmax in patients during treatment with the standard approved dose.
Antibiotics & Chemotherapy Vol. 31, No. 1, 84-90 (2015)