In vitro investigation of the intraphagocytic bioactivities of ciprofloxacin and the new fluoroquinolone agents, clinafloxacin (CI-960) and PD 131628.

In this study the intraphagocytic bioactivities of the new fluoroquinolone antimicrobial agents clinafloxacin (CI-960) and PD 131628 (the active metabolite of CI-990) were investigated in vitro at final concentrations of 0.0005-0.5 microgram/ml using human neutrophils and the combination of a radiometric and a colony-counting method, which enabled us to distinguish between intracellular bacteriostatic and bactericidal mechanisms. Ciprofloxacin was included for comparison. Staphylococcus aureus (ATCC 25923) and Escherichia coli (ATCC 25922) were used as the test intraphagocytic microbial pathogens. Clinafloxacin (> or = 0.05 microgram/ml) displayed potent intraphagocytic bactericidal activity against S. aureus, while PD 131628 was merely bacteriostatic. Ciprofloxacin displayed relatively unimpressive bacteriostatic rather than bactericidal activity for S. aureus. Against E. coli, the intraphagocytic activity of clinafloxacin (0.001-0.005 microgram/ml and above) was superior to that of PD 131628 or ciprofloxacin, which were approximately equipotent. Clinafloxacin is a potent intraphagocytic bactericidal agent for both gram-positive and gram-negative bacteria.