Comparative synergistic activity of ceftriaxone-piperacillin versus ceftriaxone-netilmicin.

The effect of combination of ceftriaxone with piperacillin or netilmicin was studied in a total of 119 clinical isolates using the checkerboard titration technique. The isolates included Pseudomonas aeruginosa, Staphylococcus aureus, enterococci and various Enterobacteriaceae. Synergy was observed in all Streptococcus faecalis strains with both combinations. Whereas the ceftriaxone/netilmicin combination showed a higher rate of synergy against Pseudomonas aeruginosa, the rate of synergy against Enterobacteriaceae was the same for the two combinations. In no instance was antagonism encountered.