Relationship between vancomycin exposure and outcomes among patients with MRSA bloodstream infections with vancomycin Etest® MIC values of 1.5 mg/L: A pilot study

Data suggest that vancomycin is less effective for methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infection (BSI) with vancomycin Etest® MIC (MICEtest) ≥1.5 mg/L. No published studies have evaluated the relationship between vancomycin exposure and outcomes among patients with MRSA BSIs vancomycin MICEtest ≥1.5 mg/L. This study was a retrospective cohort of 71 hospitalized, adult, non-dialysis patients with MRSA BSIs treated with vancomycin. All but three patients had a vancomycin MICEtest of 1.5 mg/L. Achievement of CART-derived AUC24-48h of at least 550 mg*h/L (AUC24-48h/MIC of 366 mg*h/L) was associated with a lower incidence of treatment failure. In multivariate analyses, the risk ratio was 0.45 for the CART-derived AUC24-48h threshold, indicating that achievement of the CART-derived AUC24-48h threshold of 550 was associated with a 2-fold decrease in treatment failure. These findings suggest a potential association between vancomycin exposure and outcomes in patients with MRSA BSIs with MICEtest ≥1.5 mg/L. As this study was retrospective, these findings provide the basis for a future large-scale, multi-center prospective study.