The in-vitro activity of cefadroxil, and the interpretation of disc-susceptibility testing

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Abstract
Minimum inhibitory concentrations (MICs) of cefadroxil were determined for 749 defined clinically-significant bacteria isolated in a London teaching hospital and for 63 strains from an international collection of Gram-negative bacilli. Assuming a breakpoint of 16 mg/1, for the hospital isolates 81.8% of Gram-negative bacilli and 83.4% of Gram-positive cocci were sensitive. No significant difference between in-patient, out-patient or community-acquired isolates was found. Ninety-five and a half per cent of Escherichia coli, Klebsiella aerogenes (including gentamicin-resistant strains), Proteus mirabilis, and (with the exception of Streptococcus faecalis and methicillin-resistant Staphylococcus aureus) all Gram-positive cocci were sensitive. Of 41 strains of Enterobacter spp., were resistant. Most indole-positive Proteus, and all Serratia and Acinetobacter spp. were resistant, including 36 additional strains taken from an international collection. Of 30 strains of Haemophilus influenzae, only six had MICs of 16 mg/1 or less. For disc susceptibility testing, the standard disc containing 30 μg of cefadroxil reliably gave zones of > 17 mm for organisms with MICs of < 16 mg/l. A zone of < 14 mm corresponded to MICs of > 64 mg/l. Despite a lack of controlled clinical trials, the results of this study (taken with favourable pharmacokinetics) suggest that cefadroxil has potential as an oral cephalosporin in hospital practice in the U.K.