In vitro antistaphylococcal activity of pefloxacin alone and in combination with other antistaphylococcal drugs.

MICs of pefloxacin and nine antistaphylococcal drugs were determined for 200 isolates of Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus haemolyticus, Staphylococcus hominis, and Staphylococcus saprophyticus. All the strains were susceptible to pefloxacin, vancomycin, and rifampin. Oxacillin-resistant strains were uniformly resistant to cephalothin and were more likely to be resistant to gentamicin, erythromycin, clindamycin, doxycycline, and trimethoprim-sulfamethoxazole than were oxacillin-susceptible strains. Time-kill studies with 23 strains of S. aureus, S. epidermidis, and S. haemolyticus indicated that the relative order of bactericidal activities was gentamicin greater than or equal to pefloxacin greater than oxacillin greater than vancomycin greater than rifampin. Pefloxacin combined with oxacillin or vancomycin killed staphylococci more rapidly than oxacillin or vancomycin alone but less rapidly than pefloxacin alone. Gentamicin combined with oxacillin, vancomycin, or pefloxacin resulted in the most rapid killing of gentamicin-susceptible strains. Rifampin combined with oxacillin, vancomycin, or pefloxacin reduced the bactericidal activities of those drugs, but rifampin resistance was not observed as it was with rifampin alone. Pefloxacin is a potentially useful antistaphylococcal agent.