Measurement of bactericidal activity in body fluids as a clinical research procedure

Bactericidal activity and killing rate of serum in volunteers receiving ciprofloxacin alone or in combination with vancomycin

Ten healthy volunteers received the following regimen on different days: vancomycin, 500 mg intravenously; ciprofloxacin, 200 mg intravenously; vancomycin plus ciprofloxacin. Concentrations in serum measured microbiologically at the end of infusion and 1 and 6 h after the end of infusion were, respectively (mean [standard deviation] in milligrams per liter): 32.3 (5.5), 14.2 (2.6), and 4 (0.9) for vancomycin and 3.12 (0.86), 0.78 (0.18), and 0.19 (0.05) for ciprofloxacin. Vancomycin concentration was not affected by the simultaneous administration of ciprofloxacin. The serum bacteriostatic and bactericidal (SBA) activities were measured 1 and 6 h after the end of infusion against five strains each of Staphylococcus aureus susceptible and resistant to oxacillin, Staphylococcus epidermidis susceptible and resistant to oxacillin, Corynebacterium strain JK, and Listeria monocytogenes and three strains of Mycobacterum fortuitum. Ciprofloxacin alone provided low SBAs against the tested strains even 1 h after administration. Vancomycin provided adequate SBAs against staphylococci and Corynebacterium strain JK 1 h after administration. None of the regimens tested showed adequate bactericidal activity against L. monocytogenes and M. fortuitum. The combination of vancomycin with ciprofloxacin was indifferent. This was confirmed by studying the rate of killing in serum. Vancomycin plus ciprofloxacin appeared to be promising for the empiric treatment of infection in immunocompromised patients.