Clinical efficacy of a synergistic combination of cefotaxime and amikacin against multiresistant Pseudomonas and Serratia infections.

The synergistic activity of cefotaxime and amikacin against 21 highly resistant Pseudomonas aeruginosa and Serratia marcescens isolates was evaluated in-vitro by the checkerboard tube dilution method and in-vivo in five patients with serious infections caused by these organisms. All isolates were resistant to gentamicin, tobramycin, amikacin, and cefotaxime. Synergy was observed in 90% of isolates and occurred when the MIC of amikacin was less than 256 mg/l and of cefotaxime less than 1024 mg/l. A clinical response occurred in 100% and bacteriological cure in 80% of patients. Our results demonstrate a high degree of synergism between amikacin and cefotaxime in-vitro and clinical efficacy in the treatment of infections due to multiply-resistant Pseudomonas and Serratia species.