Daptomycin

Daptomycin is a lipopeptide antibiotic with rapid in vitro bactericidal activity against gram-positive organisms. In Vitro: Daptomycin has excellent in-vitro inhibitory and bactericidal activity against nafcillin-susceptible and resistant staphylococci (MIC₉₀ less than or equal to 0.5 mg/L) and against enterococci (MIC₉₀ less than or equal to 2.0 mg/L). Daptomycin is more active than vancomycin against the majority of isolated tested. With the exception of trimethoprim-sulphamethoxazole, daptomycin is the most active agent in vitro against enterococci, and is the most active against nafcillin-resistant staphylococci. Daptomycin and vancomycin show a marked increase in MIC when the inoculum is increased from 10⁵ to 10⁷ cfu/mL^[1]. Daptomycin is effective within a very narrow range of drug concentrations (from 0.125 to 2.0 tLg/mL) and is more active than other agents tested against S. faecalis^[2]. Daptomycin inhibits the formation of these nucleotide-linked intermediates^[3]. In Vivo: At a dose of 10 mg/kg given twice daily, daptomycin reduces the number of organisms per kidney significantly compared with that in infected untreated controls within 48 h after the initiation of therapy. At 20 mg/kg given once a day, daptomycin is less effective but reduces colony counts significantly after 4 days of therapy, and its activity is comparable to that of vancomycin or vancomycin-gentamicin given twice daily^[2].