title: Mutant prevention concentrations of daptomycin for Enterococcus faecium clinical isolates.
abstract: Owing to the emergence of vancomycin-resistant Enterococcus faecium, treatment of enterococcal infections has become challenging. Although spontaneous in vitro resistance frequencies are low, the emergence of resistance is increasingly reported during daptomycin therapy. The mutant selection window (MSW), comprised between the minimum inhibitory concentration (MIC) and the mutant prevention concentration (MPC), corresponds to the concentration range within which resistant mutants may be selected. Since no data are available for enterococci, the aim of this study was to determine MPCs and MSWs for 12 representative E. faecium clinical isolates. MICs and MPCs were determined by broth microdilution and agar dilution methods, respectively. A basic MSW-derived pharmacodynamic analysis was also performed using mean maximum plasma concentration (Cmax) values obtained with dosages from 4 to 12 mg/kg. MICs and MPCs of daptomycin ranged from 0.5 to 4 mg/L and from 2 to 32 mg/L, respectively, with no correlation between them. The wideness of MSWs ranged from 2× to 32× MIC. Mean plasma Cmax values of daptomycin were calculated from 55 to 174.5 mg/L when using a dosage from 4 to 12 mg/kg. All Cmax values were above the MPCs whatever the dosage. Taking into account the protein binding of daptomycin (ca. 90%), the unbound fraction Cmax was just within the MSW in 67-92% of strains at recommended dosages (4-6 mg/kg) and was above the MPC for the majority of strains only with the highest dosage (12 mg/kg). This study shows that free daptomycin Cmax values usually fell into MSWs when using lower dosages (<10 mg/kg).
authors.affiliation: Université de Caen Normandie, EA4655 (Équipe 'Antibio-résistance'), F-14032 Caen, France.
authors.forename: Clara
authors.initials: C
authors.lastname: Sinel
authors.affiliation: Université de Caen Normandie, EA4655 (Équipe 'Antibio-résistance'), F-14032 Caen, France.
authors.forename: Clara
authors.initials: C
authors.lastname: Jaussaud
authors.affiliation: CHU de Caen, Service de Microbiologie, F-14033 Caen, France; Centre National de Référence (CNR) sur la résistance aux antibiotiques (Laboratoire associé 'Entérocoques'), F-14033 Caen, France.
authors.forename: Michel
authors.initials: M
authors.lastname: Auzou
authors.affiliation: Université de Caen Normandie, EA4655 (Équipe 'Antibio-résistance'), F-14032 Caen, France.
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Giard
authors.affiliation: Université de Caen Normandie, EA4655 (Équipe 'Antibio-résistance'), F-14032 Caen, France; CHU de Caen, Service de Microbiologie, F-14033 Caen, France; Centre National de Référence (CNR) sur la résistance aux antibiotiques (Laboratoire associé 'Entérocoques'), F-14033 Caen, France. Electronic address: cattoir-v@chu-caen.fr.
authors.forename: Vincent
authors.initials: V
authors.lastname: Cattoir
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D017576:Daptomycin / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D016984:Enterococcus faecium / Q000187:drug effects* / Q000302:isolation & purification; D016908:Gram-Positive Bacterial Infections / Q000382:microbiology*; D006801:Humans; D008826:Microbial Sensitivity Tests; D009154:Mutation; D012641:Selection, Genetic
chemical_list: D000900:Anti-Bacterial Agents; D017576:Daptomycin
keywords: Daptomycin; Enterococcus faecium; MPC; MSW; Mutant prevention concentration; Mutant selection window