Optimal vancomycin AUC24/MIC ratio for predicting clinical outcomes in patients with glycopeptide-susceptible Enterococcus faecium bacteremia

Data on the relationship between the 24-hour area under the concentration–time curve to the minimum inhibitory concentration (AUC24/MIC) and clinical outcomes in glycopeptide-susceptible Enterococcus faecium (GSEF) bacteremia remain limited. This study aimed to determine the optimal vancomycin AUC24/MIC threshold associated with treatment outcomes in patients with GSEF bacteremia. We retrospectively reviewed cases of GSEF bacteremia treated with vancomycin at a single tertiary care hospital between April 1, 2010, and March 31, 2024. Vancomycin AUC24 was estimated using a Bayesian approach, and MIC values were determined by Etest. The primary outcome was treatment failure, defined as a composite of 30-day all-cause mortality and microbiological failure (persistence of bacteremia in follow-up blood cultures). A total of 67 patients were included, and treatment failure occurred in 11 (16.4%). Classification and regression tree (CART) analysis identified an AUC24/MICEtest threshold of ≥ 427 as a predictor for reduced treatment failure. In multivariable logistic regression, achieving AUC24/MICEtest ≥427 was independently associated with reduced treatment failure (odds ratio, 0.056; 95% confidence interval, 0.003–0.35; P = 0.01). These findings indicate that achieving a vancomycin AUC24/MICEtest ≥427 was associated with reduced treatment failure in GSEF bacteremia. Larger prospective studies are needed to validate this pharmacokinetic/pharmacodynamic target.