Successful management of methicillin-resistant Staphylococcus aureus bacteremia unresponsive to vancomycin by adding fosfomycin: A case report

Abstract

Background: Vancomycin is the drug of choice for the treatment of methicillin-resistant Staphylococcus aureus (MRSA) bacteremia. However, vancomycin treatment failures are occasionally observed with some strains that are considered susceptible to vancomycin according to Clinical and Laboratory Standards Institute breakpoints (vancomycin minimum inhibitory concentration [MIC] ≤ 2 μg/mL). Although fosfomycin has in vitro activity against MRSA, clinical data regarding the use of fosfomycin either alone or in combination for the management of MRSA bacteremia is limited. Case Report: A 57-year-old woman who was on regular hemodialysis for chronic kidney disease presented with sepsis associated with possible infection of arteriovenous fistula. Blood culture grew MRSA with vancomycin MIC of 1.5 μg/mL. Despite placement of a double-lumen catheter for hemodialysis and treatment with vancomycin and serum concentrations monitoring to keep trough levels of 15 to 20 μg/mL, her blood cultures still continued to grow MRSA for over 10 days. Later, intravenous fosfomycin was added to the regimen along with vancomycin. After three days of this combination, suppression of bacteremia was achieved. Conclusion: Combination of fosfomycin and vancomycin might be another option for the treatment of bacteremia due to MRSA with vancomycin MIC of 1.5 μg/mL that is not responsive to vancomycin alone.