Reassessment of cefaclor breakpoints for Haemophilus influenzae

Fiona MacKenzie, K. E. Milne, Ian M Gould

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    We previously reported that standard methods overestimate celaclor minimum inhibitory concentrations (MICs) for Streptococcus pneumoniae due to in vitro chemical instability. This study aimed to ascertain if standard methods accurately measure cefaclor MICs to Haemophilus influenzae. Cefuroxime was used as a comparator.

    Standard NCCLS broth microdilution and E-Test MICs were determined for eight isolates of H. influenzae. Kill curves determined the "bacteriostatic" MIC, defined as the concentration showing no significant growth or kill over six hours taking into account cefaclor instability.

    On average, cefaclor and cefuroxime bacteriostatic MICs were 0.2 x MIC and 0.6 x MIC determined by NCCLS methodology respectively. The mean MIC determined by NCCLS methodology was 3.0 mg/L for cefaclor and 0.8 mg/L for cefuroxime.

    Cefaclor MICs by NCCLS methodology were overestimated due to chemical instability over 18-24 hours. The bacteriostatic MICs by kill curve were not significantly different from those of cefuroxime.

    Original languageEnglish
    Pages (from-to)329-333
    Number of pages4
    JournalJournal of Chemotherapy
    Issue number4
    Publication statusPublished - 2004


    • cefaclor
    • Haemophilus influenzae
    • MICs


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