In vitro activity of ciprofloxacin against gram-positive cocci.

In vitro studies compared the activities of ciprofloxacin, vancomycin, and fusidic acid against staphylococci, streptococci, and enterococci. Against 111 methicillin-resistant and 162 methicillin-susceptible staphylococcal strains, fusidic acid was the most potent of the three drugs (minimal inhibitory concentration [MIC] for 90 percent of the strains was 0.06 microgram/ml). Ciprofloxacin and vancomycin were also effective anti-staphylococcal drugs (MIC of ciprofloxacin for 90 percent of the strains was 0.5 microgram/ml and of vancomycin was 1.0 microgram/ml). Ciprofloxacin had a more rapid bactericidal effect against staphylococci than did vancomycin. Neither vancomycin nor ciprofloxacin alone had useful bactericidal activity against enterococci. Streptococci were only marginally susceptible to ciprofloxacin (MIC for 90 percent of the strains was 1.0 to 4.0 micrograms/ml for different species). Vancomycin was superior to ciprofloxacin in its anti-streptococcal activity (MIC for 90 percent of the strains was 0.25 to 0.5 microgram/ml). The promising in vitro anti-staphylococcal activity of ciprofloxacin deserves further consideration in clinical trials.