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Antimicrobial Agents and Chemotherapy, December 2002, p. 3782-3789, Vol. 46, No. 12
0066-4804/02/$04.00+0 DOI: 10.1128/AAC.46.12.3782-3789.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Laboratoire d'Antibiologie, Institut de Bactériologie, Université Louis Pasteur, Hôpitaux Universitaires de Strasbourg, F67000 Strasbourg, France,1 SmithKline Beecham Pharmaceuticals, Collegeville, Pennsylvania2
Received 30 March 2001/ Returned for modification 22 November 2001/ Accepted 29 August 2002
The objective of the present study was to investigate the potential bactericidal activity of amoxicillin-clavulanate against ß-lactamase-producing Escherichia coli strains and to elucidate the extent to which enzyme production affects the activity. Six adult Yucatan miniature pigs received a single intravenous dose of 1.1 g of amoxicillin-clavulanate as an intravenous infusion over 30 min. The pharmacokinetic parameters were determined for the serum samples and compared to the published data for humans (2.2-g intravenous dose). The parameters were comparable for the two species, and therefore, the miniature pig constitutes a good model for pharmacodynamic study of amoxicillin-clavulanate. Therefore, the model was used in an ex vivo pharmacodynamic study of amoxicillin-clavulanate against four strains of Escherichia coli producing ß-lactamases at different levels. The E. coli strains were cultured with serial dilutions (1:2 to 1:256) of the serum samples from the pharmacokinetic study, and the number of surviving bacteria was determined after 1, 3, and 6 h of exposure. Amoxicillin-clavulanate at concentrations less than the MIC and the minimal bactericidal concentration had marked bactericidal potency against the strain that produced low levels of penicillinase. For high-level or intermediate-level ß-lactamase-producing strains, the existence of a clavulanate concentration threshold of 1.5 to 2 µg/ml, below which there was no bactericidal activity, was demonstrated. The index of surviving bacteria showed the existence of mixed concentration- and time-dependent actions of amoxicillin (in the presence of clavulanate) which varied as a function of the magnitude of ß-lactamase production by the test strains. This study shows the effectiveness of amoxicillin-clavulanate against low- and intermediate-level penicillinase-producing strains of E. coli. These findings are to be confirmed in a miniature pig experimental infection model.
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