title: Susceptibility of Haemophilus influenzae to amoxicillin/clavulanic acid, erythromycin, cefaclor, and trimethoprim/sulfamethoxazole.
abstract: A total of 126 strains of Haemophilus influenzae were examined for susceptibility to amoxicillin/clavulanic acid, trimethoprim/sulfamethoxazole, cefaclor, and erythromycin by an agar dilution procedure. Fifty strains (eight type B, 42 non-type B), all with ampicillin minimal inhibitory concentrations (MIC) of greater than or equal to 6.2 micrograms/ml, produced beta-lactamase. The remaining 76 strains (18 type B, 59 non-type B) were beta-lactamase-negative. All of these strains had ampicillin MICs of less than or equal to 0.8 micrograms/ml. The combination of amoxicillin and clavulanic acid (2:1) was highly active against all strains tested. With the exception of two strains with amoxicillin/clavulanic acid MICs of 1.6/0.8 ug/ml, all strains were inhibited by concentrations of less than or equal to 0.8/0.4 ug/ml. Trimethoprim/sulfamethoxazole was also found to be highly active (MICs uniformly less than or equal to 0.1/1.9 ug/ml). Cefaclor and erythromycin were the least active of the agents tested. Fourteen strains (10.6%) had cefaclor MICs of greater than 32 ug/ml. Forty-seven strains (35.6%) had erythromycin MICs of greater than 8 micrograms/ml. With the exception of amoxicillin/clavulanic acid beta-lactamase production did not seem to influence the activity of any of the antimicrobials tested. Minimum inhibitory concentrations of amoxicillin/clavulanic acid, although still well within achievable serum levels, were approximately one twofold dilution higher with beta-lactamase-producing H. influenzae type B strains than with beta-lactamase-negative strains.
mesh_terms: D000658:Amoxicillin / Q000494:pharmacology; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002433:Cefaclor / Q000494:pharmacology; D002648:Child; D002675:Child, Preschool; D019818:Clavulanic Acid; D002969:Clavulanic Acids / Q000494:pharmacology; D004338:Drug Combinations / Q000494:pharmacology; D004917:Erythromycin / Q000494:pharmacology; D006193:Haemophilus influenzae / Q000187:drug effects* / Q000302:isolation & purification; D006801:Humans; D007223:Infant; D008826:Microbial Sensitivity Tests; D013420:Sulfamethoxazole / Q000494:pharmacology; D014295:Trimethoprim / Q000494:pharmacology; D015662:Trimethoprim, Sulfamethoxazole Drug Combination
chemical_list: D000900:Anti-Bacterial Agents; D002969:Clavulanic Acids; D004338:Drug Combinations; D019818:Clavulanic Acid; D004917:Erythromycin; D002433:Cefaclor; D000658:Amoxicillin; D015662:Trimethoprim, Sulfamethoxazole Drug Combination; D014295:Trimethoprim; D013420:Sulfamethoxazole