Antibacterial Activity of a New Parenteral Cephalosporin—HR 756: Comparison with Cefamandole and Ceforanide

HR 756, a new parenteral cephalosporin that is beta-lactamase resistant, was tested against 271 bacterial isolates. Both agar and broth dilution testing were employed, using two media and two inoculum sizes of bacteria. Antibacterial activity of the drug was compared to that of cefamandole (CFM) and ceforanide (CFN). In agar, HR 756 was more active than CFM and CFN against all bacteria tested except isolates of Staphylococcus aureus, which were better inhibited by CFM. HR 756 exhibited some antipseudomonas activity in agar, although a marked inoculum effect was apparent. A comparison of median minimum inhibitory and bactericidal concentrations in broth showed again that HR 756 was the most active of these three drugs. HR 756 demonstrated enhanced antibacterial activity compared to CFM and CFN against bacteria sensitive to all three drugs as well as against more resistant isolates of Serratia marcescens, Enterobacter species, and indole-positive Proteus. As with other cephalosporins, results for most bacteria were affected by inoculum size, medium, and type of dilution test employed in in vitro studies.