1065 CHLORAMPHENICOL KILLS H. INFLUENZA MORE RAPIDLY THAN AMPICILLIN

Abstract

Although a combination of chloramphenicol (CHL) plus a penicillin is the inital therapy for H. influenza type B (H flu) meningitis, it is not known whether the combination, CHL alone, or ampicillin (AMP) alone is most effective against AMP sensitive H flu. We, therefore, studied the bactericidal effects of these agents against H flu isolated from blood or CSF of 21 infants. Cultures contained 105 CFU in 1 or 10ml Mueller-Hinton broth with supplement C. Over 90% of isolates were killed by 18h incubation with 3μg/ml CHL or 3μg/ml AMP. The median time to kill 99.99% of the inoculum was only 5.8h for 20μg/ml CHL in contrast to 17.4h for 20μg/ml AMP. The combination of 20μg/ml each CHL plus AMP produced 99.99% killing in a median time of 5.6h, indicating that AMP did not significantly retard the rapid bactericidal action of CHL. In checkerboard titrations, CHL increased the minimal bactericidal concentration of AMP 4-fold or more for 6 isolates, but AMP influenced the bactericidal effect of CHL in only one isolate. Although CHL can increase the AMP concentration required for AMP bactericidal effects, CHL has a much more rapid bactericidal action, and is as effective gravimetrlcally as AMP. Therefore, the combined use of CHL plus AMP may be more effective than AMP alone and as effective as CHL alone for H flu.