Author(s): Sharma M, Riederer K, Chase P, Khatib R
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Abstract Daptomycin is bactericidal against Staphylococcus aureus, with susceptibility defined as a minimal inhibitory concentration (MIC) < or =1 microg/ml. Higher MIC developed in a few cases during therapy. The frequency of MIC rise in persistent bacteremia is unknown. We evaluated all patients with S. aureus bacteremia (SAB) treated with daptomycin (> or =2 days) from 1 April 2004 to 30 October 2006. All patients with post-daptomycin-exposure saved isolates were studied. Daptomycin susceptibility was determined (in duplicate) on all pre- and post-daptomycin-exposure isolates by the broth (Mueller-Hinton) microdilution method. Among 74 treatment courses in 67 patients, 18 were for SAB. Ten had persistent bacteremia (median = 11 days; range = 1-21) and post-daptomycin-exposure saved isolates. The patient age was 29-84 years (median = 57.5 years). Intravascular catheter was the most common source (50\%). Most patients (90\%) failed therapy prior to starting daptomycin. The initial daptomycin dose was 4 mg/kg in four (40\%) cases. The pre-exposure MIC was 0.125-0.5 microg/ml. The post-exposure MIC increased in four cases and was elevated in two cases (60\%), to 2 microg/ml in five and 4 microg/ml in one. MIC rise was noted within 5-15 days of exposure and persisted up to 247 days after stopping daptomycin. Pulse-field gel electrophoresis (PFGE) band pattern of isolates with increased MIC revealed 1-3-band differences, implying genetic relatedness. All patients with non-susceptible isolates relapsed or failed therapy. These findings illustrate that daptomycin susceptibility often decreases during the treatment of persistent SAB. Therefore, susceptibility should be closely monitored during therapy.
This article was published in Eur J Clin Microbiol Infect Dis
and referenced in Clinical Microbiology: Open Access