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Authors: Marty Allen, MD, James Summersgill, PhD, Craig Roberts, MD, David Seligson, MD; Julio Ramirez, MD, University of Louisville, Louisville, KY

Title: Distribution of Serum Killing Levels for Vancomycin and Daptomycin in Patients with MRSA Osteomyelitis

Purpose: In order to optimize antibiotic therapy in the management of patients with MRSA osteomyelitis our group performs serum bactericidal levels. The objective of this study was to compare the serum killing levels obtained with vancomycin vs. Daptomycin.

Methods: Observational study of patients with MRSA osteomyelitis treated at the University of Louisville Hospital. Patients with killing levels against MRSA isolates tested for both vancomycin and daptomycin were reviewed. Serum bactericidal test was performed at the Infectious Diseases Reference Laboratory at University of Louisville. Patient peak serum samples were obtained 1 hour after antibiotic infusion and serially diluted with Mueller-Hinton broth. Each dilution was inoculated with 5X105 CFU/ml and allowed to incubate for 18-24 hours. The serum bactericidal titer was defined as the highest dilution demonstrating 99.9% kill rate on 48 hour subcultures of the final inoculum.

Results: We identified 11 patients with MRSA osteomyeltis that recieved doses of both vancomycin and daptomycin separately. The serum killing levels for both vancomycin and daptomycin in these patients are shown in figure 2.

Discuassion and Conclusion: This study indicates that daptomycin achieves significantly higher serum bactericidal activity for MRSA isolates in patients with osteomyelitis. This may translate into more effective eradication of MRSA from bone biofilms. Further studies comparing antibiotics for MRSA osteomyelitis and coorelating with clinical outcomes with serum bactericidal levels need to be performed.

Musculoskeletal Infecton Society
Musculoskeletal Infecton Society