Recent Vancomycin Use: Effect on MRSA MICs

Vancomycin MICs were increased and bactericidal activity was reduced in isolates from patients with MRSA bacteremia who had used vancomycin within the previous 30 days.

Recent antimicrobial exposure is a recognized risk factor for reduced susceptibility; however, the effects of previous vancomycin use in patients with methicillin-resistant Staphylococcus aureus (MRSA) bacteremia are unknown. To explore this issue, investigators (one of whom receives research funding from the manufacturer of daptomycin) examined vancomycin and daptomycin MICs and killing activity in isolates from such patients.

MRSA bloodstream isolates from 81 patients were arbitrarily selected from samples collected between 1998 and 2003 as part of phase III/IV studies. Thirty-eight patients had vancomycin exposure during the previous 30 days; 43 had no documented exposure within this time frame.

All strains were vancomycin susceptible acco…

Reviewing Author

Lynn L. Estes, PharmD