In vitro activities of co-amoxiclav at concentrations achieved in human serum against the resistant subpopulation of heteroresistant Staphylococcus aureus: A controlled study with vancomycin

Abstract

The effects of concentrations that simulated those in human serum after a single intravenous dose of amoxicillin (2 g), amoxicillin-clavulanic acid (2,000 and 200 mg, respectively), or vancomycin (500 mg), on the viability and β-lactamase activity of two isogenic (β-lactamase and non-β-lactamase producer) heteroresistant Staphylococcus aureus strains were studied in an in vitro pharmacodynamic model. A reduction of ≤97% of the initial inoculum was obtained with vancomycin and amoxicillin-clavulanic acid against both strains, with respect to the total bacterial population and the oxacillin- resistant subpopulation. The same pattern was observed with amoxicillin and the β-lactamase-negative strain. β-Lactamase activity in the β-lactamase- positive strain changed over time parallel to viability, decreasing with amoxicillin-clavulanic acid or vancomycin and increasing in the amoxicillin and control groups. Clavulanic acid concentrations achievable in serum that changed over time allowed amoxicillin to act against the β-lactamase- producing methicillin-resistant S. aureus to a similar extent as vancomycin.