title: Relationship between susceptibility to daptomycin in vitro and activity in vivo in a rabbit model of aortic valve endocarditis.
abstract: Daptomycin is approved for treatment of Staphylococcus aureus bacteremia and right-sided endocarditis. Increases in daptomycin MICs have been associated with failure. A rabbit model of aortic valve endocarditis was used to determine whether MIC correlates with activity in vivo and whether a higher daptomycin dose can improve efficacy. Two related clinical S. aureus strains, one with a daptomycin MIC of 0.5 microg/ml and the other with a MIC of 2 microg/ml, were used to establish aortic valve endocarditis in rabbits. Daptomycin was administered once a day for 4 days at 12 mg/kg of body weight or 18 mg/kg to simulate doses in humans of 6 mg/kg and 10 mg/kg, respectively. Endocardial vegetations, spleens, and kidneys were harvested and quantitatively cultured. The strain with a MIC of 2 microg/ml had a survival advantage over the strain with a MIC of 0.5 microg/ml with >100 times more organisms of the former in endocardial vegetations at the 12-mg/kg dose in a dual-infection model. Both the 12-mg/kg dose and the 18-mg/kg dose completely eradicated the strain with a MIC of 0.5 from vegetations, spleens, and kidneys. The 12-mg/kg dose was ineffective against the strain with a MIC of 2 in vegetations; the 18-mg/kg dose produced a reduction of 3 log(10) units in CFU in vegetations compared to the controls, although in no rabbit were organisms completely eliminated. Increasing the dose of daptomycin may improve its efficacy for infections caused by strains with reduced daptomycin susceptibility.
authors.affiliation: San Francisco General Hospital, University of California San Francisco, San Francisco, California 94110, USA. hchambers@medsfgh.ucsf.edu
authors.forename: H F
authors.initials: HF
authors.lastname: Chambers
authors.forename: L
authors.initials: L
authors.lastname: Basuino
authors.forename: B A
authors.initials: BA
authors.lastname: Diep
authors.forename: J
authors.initials: J
authors.lastname: Steenbergen
authors.forename: S
authors.initials: S
authors.lastname: Zhang
authors.forename: P
authors.initials: P
authors.lastname: Tattevin
authors.forename: J
authors.initials: J
authors.lastname: Alder
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001021:Aortic Valve; D019540:Area Under Curve; D017576:Daptomycin / Q000493:pharmacokinetics / Q000494:pharmacology* / Q000627:therapeutic use; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D004697:Endocarditis, Bacterial / Q000188:drug therapy*; D006349:Heart Valve Diseases / Q000188:drug therapy; D008826:Microbial Sensitivity Tests; D011817:Rabbits; D013203:Staphylococcal Infections / Q000188:drug therapy*; D013211:Staphylococcus aureus / Q000187:drug effects
chemical_list: D000900:Anti-Bacterial Agents; D017576:Daptomycin