Abstract
The interaction of ampicillin and chloramphenicol against Haemophilus influenzae was studied because the combination is commonly used as initial therapy for meningitis and because little information was available about in vitro synergy or antagonism. Two dimensional ‘checkerboard’ dilutions of drugs were made in Mueller-Hinton broth containing 2% supplement C using a micro-titer apparatus. The minimal inhibitory concentration (MIC) was the smallest concentration of antibiotic(s) preventing a visible button of growth after incubation at 37C for 18h. Synergy, determined by isobolograms made from MICs, occurred against 6 of 13 ampicillin-susceptible and against 5 of 8 ampicillin-resistant H. influenzae type b isolates using 104 CFU/ml. Using a large inoculum of 107 CFU/ml, synergy occurred against 9 of 13 ampicillin-susceptible and against 2 of 8 resistant strains. Additive effects were observed against the remainder of the type b strains and against single isolates of chloramphenicol-resistant nontypable H. influenzae and H. parainfluenzae. These data indicate that ampicillin and chloramphenicol may be synergistic against a significant number of H. influenzae isolates depending upon inoculum size, and antagonism did not occur. They support the recommendation that both be used as initial therapy for patients with suspected H. influenzae meningitis.
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Feldman, W., Nelson, J. SYNERGY OF AMPICILLIN AND CHLORAMPHENICOL AGAINST HAEMOPHILUS INFLUENZAE. Pediatr Res 11, 499 (1977). https://doi.org/10.1203/00006450-197704000-00776
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DOI: https://doi.org/10.1203/00006450-197704000-00776