Proposed disc zone breakpoints for doripenem for use with the BSAC disc susceptibility testing method

Abstract

Sir, Doripenem is a new carbapenem, recently licensed in the European Union for treatment of nosocomial pneumonia (including ventilator-associated pneumonia), complicated intraabdominal infections and complicated urinary tract infections. A 10 mg doripenem disc has been proposed for routine susceptibility testing. We determined provisional zone breakpoints corresponding to European Committee on Antimicrobial Susceptibility Testing (EUCAST) MIC breakpoints for these 10 mg doripenem discs in the BSAC disc method. Isolates (n1⁄4810) were selected from the BSAC Bacteraemia Resistance Surveillance Project (2005–06), supplemented with additional, more-resistant, isolates from other survey collections and reference submissions held by the UK HPA’s Antibiotic Resistance Monitoring and Reference Laboratory. Care was taken, whenever possible, to select isolates for which the MICs corresponded with or were within one or two dilutions of the breakpoints. Zones and agar dilution MICs were determined by the BSAC methods. Results were reviewed against EUCAST/ European Medicines Agency (EMEA) MIC breakpoints, as also adopted by the BSAC, of: susceptible, ≤1 mg/L and resistant, .1 mg/L for streptococci; and susceptible, ≤1 mg/L and resistant, .4 mg/L for staphylococci, enterococci, Enterobacteriaceae, Acinetobacter spp. and Pseudomonas spp. Error minimization was used to optimize the values. Zone breakpoints corresponding to these MIC breakpoints were as follows: