Comparative study of serum bactericidal activity of cefotaxime alone or in combination with tobramycin.

The objectives of this study were to investigate the bactericidal activity in serum of cefotaxime alone or in combination with tobramycin against clinical strains and to determine the influence of tobramycin on the pharmacokinetics of cefotaxime. The peak bactericidal activity in serum of cefotaxime alone against Klebsiella oxytoca, Enterobacter aerogenes, Serratia marcescens, Pseudomonas cepacia, and Listeria monocytogenes varied between 1:4 and 1:256. Bactericidal activity could still be detected at 6 h against K. oxytoca and L. monocytogenes. The addition of tobramycin increased the bactericidal activity of cefotaxime against E. aerogenes from 1:16 to 1:128 (P less than 0.01). Cefotaxime recovery from urine was significantly decreased when tobramycin was added. Our data are comparable with those of other investigators who have shown a limited increase in the bactericidal activity of cefotaxime when aminoglycosides are added.