The effectiveness of daptomycin versus vancomycin for treating experimental methicillin-susceptible (MSSA) and methicillin-resistant Staphylococcus aureus (MRSA) catheter-related infection by antibiotic-lock technique was assessed.

One MSSA strain and one clinical MRSA isolate were used. A preliminary in vitro study determined the minimum biofilm eradication concentration (MBEC) of vancomycin and daptomycin. An intravenous catheter was implanted in New Zealand white rabbits. Infection was induced by 24 h locking the catheter with 0.3 mL of broth culture containing MSSA or MRSA. The 24 h of antibiotic-lock treatment groups were: control, vancomycin 10 mg/mL, daptomycin 5 mg/mL and daptomycin 50 mg/mL.

Daptomycin showed greater in vitro activity than vancomycin against biofilm bacteria (MBECs of vancomycin and daptomycin for MSSA, >2000 mg/L and 7 mg/L; MRSA, >2000 mg/L and 15 mg/L). Daptomycin 5 mg/mL achieved significant reductions relative to vancomycin 10 mg/mL in log₁₀ cfu recovered from catheter tips for both strains (P < 0.05). Only daptomycin 50 mg/mL achieved negative catheter tip cultures (up to 75% in MSSA and 85% in MRSA, P < 0.05), showing the greatest median log₁₀ cfu reduction compared to controls (6.07 in MSSA and 6.59 in MRSA, P < 0.05).

Daptomycin 50 mg/mL showed the highest activity against both strains biofilms.