Effect of the Minimum Inhibitory Concentration of Vancomycin on the Clinical Outcome of Enterococcus faecium Bacteremia

Abstract

Background/aim: Vancomycin (VCM) is an antibiotic widely used in the treatment of resistant bacteria. In patients with methicillin-resistant Staphylococcus aureus (MRSA) infection, the clinical outcome differs according to the VCM minimum inhibitory concentration (MIC) of isolates. However, the effect of VCM MIC on the clinical outcome is unclear for bacterial species other than MRSA. This study evaluated the relationship between the VCM MIC and clinical outcomes in patients with Enterococcus faecium bacteremia.

Patients and methods: This study included patients who had E. faecium detected in at least one set of blood cultures between April 2011 and March 2022. The study assessed the outcome according to the VCM MIC. The primary outcome was the 30-day mortality rate. Measures of interest included the initial serum concentration of VCM, MIC, the area under the curve (AUC), and the AUC over 24-48 hours (AUC_{24-48 h}).

Results: A total of 26 patients were included in the study, of whom 5 died and 21 survived. The 30-day mortality was higher in patients with higher MICs and lower serum albumin levels. Patients with a serum albumin level <2.0 mg/dl and a MIC ≥1 μg/ml had significantly shorter survival than those who did not (p=0.013, log-rank test).

Conclusion: The 30-day mortality rate of patients with E. faecium bacteremia is associated with the VCM MIC of E. faecium isolates and the patient's nutritional status. Patients with albumin <2 mg/dl and MIC ≥1 μg/ml may have a poor outcome and require careful clinical monitoring.

Keywords: Enterococcus faecium; Vancomycin; bacteremia; clinical outcome; minimum inhibitory concentration; therapeutic drug monitoring.