Cephapirin: in vitro antibacterial spectrum.

Cephapirin, a new semisynthetic cephalosporin derivative, was found to have an antibacterial spectrum similar to that of cephalothin. Staphylococcus aureus was inhibited by cephapirin concentrations of 0.09 to 12.5 mug/ml. S. epidermidis, S. viridans, S. pyogenes, and Diplococcus pneumonia isolates were inhibited by less than 1 mug/ml. The Enterococcus required a concentration of 25 mug of antibiotic per ml for inhibition. Approximately 65% of Escherichia coli, and all Klebsiella, indole-negative Proteus, and Salmonella strains tested were inhibited by the drug. Serratia, Pseudomonas, indole-positive Proteus, and Erwinia strains were highly resistant. Inoculum size was not an important factor in determining the level of sensitivity of S. aureus to cephapirin. The antibiotic does not appear to be significantly bound to serum protein. In vitro development of resistance to the drug was demonstrated with two isolates of S. aureus.