Evaluation of antibacterial activities of cephalosporin antibiotics: cefazolin, cephaloridine, cephalothin, and cephalexin.

The antibacterial activities of 4 cephalosporin antibiotics, cefazolin, cephaloridine, cephalothin and cephalexin, against 330 isolates of bacteria from patients at National Taiwan University Hospital, were determined by an agar plate dilution technique. Cephalosporins possess strong antibacterial activity against gram-positive bacteria except Enterococci. Staphylococcus aureus is the most susceptible among the organisms tested. More than 90% of Staphylococcus aureus strains are suppressed by cefazolin, cephaloridine and cephalothin at the concentrations of 3.13 mug/ml or less, except that 49.1% are suppressed by cephalexin. The relative potency of cephalosporins against Staphylococcus aureus in decreasing order is cephaloridine, cephalothin, cefazolin, and cephalexin. The gram-negative bacilli, Escherichia coli, Klebsiella pneumoniae and Proteus mirabilis are less susceptible to cephalosporins than the gram-positive cocci. Among the cephalosporins, cefazolin is the most active against the gram-negative pathogens tested. The relative potency of antibacterial activity of cephalosporins against E. coli in decreasing order is cefazolin, cephaloridine, cephalexin, and cephalothin. One hour after the intramuscular injection of 500 mg of cefazolin, the maximum concentration of 33.3 mug/ml is reached in the serum. The sufficient high levels are sustained for 8 hours. Very high concentrations of cefazolin are also found in the urine.