In vitro bacteriostatic and bactericidal activities of 7 cephalosporin antibiotics on Haemophilus influenzae.

A total of 30 recently isolated strains of Haemophilus influenzae were tested for in vitro susceptibility to seven cephalosporins. In order of bacteriostatic effectiveness, the in vitro activity of the antibiotics studied was: cephapirin (median MIC = 0.78 mcg/ml), cephalothin (median MIC = 1.56 mcg/ml), cefazolin (median MIC: 1.56 mcg/ml), cephaloridine (median MIC = 3.12 mcg/ml), cefoxitin (median MIC = 3.12 mcg/ml), cephradine (median MIC = 12.5 mcg/ml) and cephalexin (median MIC = 25 mcg/ml). The bactericidal effectiveness of the seven compounds was studied against one of these strains. No drug was able to kill the selected strain in less than 6 hrs, even at 100 mcg per ml. Cefoxitin exhibited the best bactericidal effects, closely followed by cefazolin and cephapirin.