| In Vitro | In vitro activity: Daptomycin (5 μg/ml) reduces cell viability by>99% and membrane potential by>90% within 30 min in Staphylococcus aureus. Daptomycin exhibits rapid in vitro bactericidal activity against clinically significant strains of gram-positive pathogens including hemolytic streptococci, methicillin-resistant Staphylococcus aureus, and vancomycin-resistant enterococci. Daptomycin acts at the cytoplasmic membrane of susceptible bacteria (8), as demonstrated by binding and fractionation studies. Daptomycin also differs from that of some antimicrobial peptides (e.g., human neutrophil peptide 1) that are capable of rapid depolarization of the cytoplasmic membrane but do not induce cell death for 1 hour to 2 hours. Daptomycin inserts into the cytoplasmic membrane of bacteria, as indicated by whole-cell and artificial membrane studies. Daptomycin demonstrates greater bactericidal activity than all other drugs tested, killing ≥3 log CFU/ml by 8 hours. Daptomycin is a cyclic polypeptide derived from Streptomyces roseosporus and representing a class of antimicrobial agents known as the peptolides (acid lipopeptide antibiotics). Daptomycin is also active against vancomycin-resistant gram-positive bacteria, including enterococci. Daptomycin is highly protein bound (94%), and its in vitro activity is altered in the presence of serum or albumin. Daptomycin consists of a 13-member amino acid cyclic lipopeptide with a decanoyl side-chain, the lipophilic Daptomycin tail into the bacterial cell membrane, causing rapid membrane depolarization and a potassium ion efflux. Daptomycin treatment has been linked to fully reversible skeletal muscle toxicity with no effect on smooth or cardiac muscle
Kinase Assay: 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. 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. Daptomycin inhibits the formation of these nucleotide-linked intermediates. |
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| Animal model | Inocula containing 109 CFU/mL are prepared from an 18-h brain heart infusion broth culture. The exact number in each inoculum is subsequently determined by the standard serial 10-fold dilution agar pour plate technique. Animals are challenged intravenously with a 1.0-mL inoculum. This inoculum is known to infect the renal medulla of normal rats. Twenty-four hours later the animals are divided into eight groups and are given either saline only (controls) or antibiotic therapy initiated with Daptomycin at 10 mg/kg (Daptomycin10), Daptomycin at 20 mg/kg (Daptomycin20), Daptomycin10 plus gentamicin at 1.5 mg/kg, vancomycin at 20 mg/kg, vancomycin at 20 mg/kg plus gentamicin at 1.5 mg/kg, ampicillin at 30 mg per rat per injection, and ampicillin at 30 mg per rat plus gentamicin at 1.5 mg/kg. Animals receive Daptomycin20 once daily; all other drugs are administered twice daily. Vancomycin and Daptomycin are given subcutaneously; ampicillin and gentamicin are given intramuscularly. Drugs are administered for up to 13 days |
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