Development of Daptomycin resistance in vivo in methicillin-resistant Staphylococcus aureus

Daptomycin is a new lipopeptide antibiotic that is rapidly bactericidal against Staphylococcus aureus. We report daptomycin resistance and treatment failure in 2 patients with osteomyelitis due to methicillin-resistant S. aureus. Disk diffusion susceptibility testing failed to detect resistance. Daptomycin at high concentration retained bactericidal activity against resistant isolates.