Response of complicated methicillin-resistant Staphylococcus aureus endocarditis to the addition of trovafloxacin

Pharmacodynamic evaluation of the intracellular activities of antibiotics against Staphylococcus aureus in a model of THP-1 macrophages

The pharmacodynamic properties governing the activities of antibiotics against intracellular Staphylococcus aureus are still largely undetermined. Sixteen antibiotics of seven different pharmacological classes (azithromycin and telithromycin [macrolides]; gentamicin [an aminoglycoside]; linezolid [an oxazolidinone]; penicillin V, nafcillin, ampicillin, and oxacillin [beta-lactams]; teicoplanin, vancomycin, and oritavancin [glycopeptides]; rifampin [an ansamycin]; and ciprofloxacin, levofloxacin, garenoxacin, and moxifloxacin [quinolones]) have been examined for their activities against S. aureus (ATCC 25923) in human THP-1 macrophages (intracellular) versus that in culture medium (extracellular) by using a 0- to 24-h exposure time and a wide range of extracellular concentrations (including the range of the MIC to the maximum concentration in serum [C(max); total drug] of humans). All molecules except the macrolides caused a net reduction in bacterial counts that was time and concentration/MIC ratio dependent (four molecules tested in detail [gentamicin, oxacillin, moxifloxacin, and oritavancin] showed typical sigmoidal dose-response curves at 24 h). Maximal intracellular activities remained consistently lower than extracellular activities, irrespective of the level of drug accumulation and of the pharmacological class. Relative potencies (50% effective concentration or at a fixed extracellular concentration/MIC ratio) were also decreased, but to different extents. At an extracellular concentration corresponding to their C(max)s (total drug) in humans, only oxacillin, levofloxacin, garenoxacin, moxifloxacin, and oritavancin had truly intracellular bactericidal effects (2-log decrease or more, as defined by the Clinical and Laboratory Standards Institute guidelines). The intracellular activities of antibiotics against S. aureus (i) are critically dependent upon their extracellular concentrations and the duration of cell exposure (within the 0- to 24-h time frame) to antibiotics and (ii) are always lower than those that can be observed extracellularly. This model may help in rationalizing the choice of antibiotic for the treatment of S. aureus intracellular infections.

Clinafloxacin for the Treatment of Bacterial Endocarditis

We report the results of a prospective, multicenter trial assessing intravenous and oral clinafloxacin treatment for infective endocarditis. Sixty-six patients constituted the final study population. Among the 53 patients with native valve infection, Staphylococcus aureus and Streptococcus viridans were the most common pathogens. Twelve patients with native valve infection required surgery, at which time all valve tissue culture results were negative. The overall success rate for native valve infection was 87%. Single valves were involved in 11 of 13 patients with prosthetic valve endocarditis (PVE), and multiple valves were involved in 2 cases. Enterococcus faecalis was the most common pathogen, causing 4 of the PVE cases. The overall success rate for treatment of PVE was 69%. Patients with PVE who did not respond to treatment presented with complications that predict poor prognosis. Clinafloxacin may be effective for both native and PVE, but further studies are indicated.