Ceftriaxone against gram-negative and gram-positive bacteria: bactericidal and post-antibiotic effect.

The effect of ceftriaxone against Gram-negative and Gram-positive strains of different clinical isolates has been compared to that of other cephalosporins such as cefuroxime, cefoxitin and cefotaxime. Cefotaxime and ceftriaxone have a notably higher activity against Enterobacteriaceae than cefuroxime and cefoxitin. If ceftriaxone activity is compared to cefotaxime activity, it may be seen that the former shows a stronger action against Pseudomonas, Proteus rettgeri, Enterobacter and Serratia. Against Staphylococcus aureus and enterococci the four antibiotics show a low level of activity. The effect of a microorganism's temporary contact with ceftriaxone was tested by a method whereby the antibiotic was removed with an ion-exchanging resin. Ceftriaxone shows rapid bactericidal activity against sensitive bacteria and if it is used at concentrations slightly higher than MIC, as in vivo against bacteria of average sensibility, we notice a 10-18 h bacteriostatic effect during which a prevalence of filamentous shapes of gram-negative bacteria is observed.