A ratio of the
vancomycin area under the concentration-time curve to the MIC (AUC/MIC) of ≥ 400 has been associated with clinical success when treating
Staphylococcus aureus pneumonia, and this target was recommended by recently published
vancomycin therapeutic monitoring consensus guidelines for treating all serious S. aureus
infections. Here,
vancomycin serum trough levels and
vancomycin AUC/MIC were evaluated in a "real-world" context by following a cohort of 182 patients with S. aureus
bacteremia (SAB) and analyzing these parameters within the critical first 96 h of
vancomycin therapy. The median
vancomycin trough level at this time point was 19.5 mg/liter. There was a significant difference in
vancomycin AUC/MIC when using broth microdilution (BMD) compared with Etest MIC (medians of 436.1 and 271.5, respectively; P < 0.001). Obtaining the recommended
vancomycin target AUC/MIC of ≥ 400 using BMD was not associated with lower 30-day all-cause or attributable mortality from SAB (P = 0.132 and P = 0.273, respectively). However, an alternative
vancomycin AUC/MIC of >373, derived using classification and regression tree analysis, was associated with reduced mortality (P = 0.043) and remained significant in a multivariable model. This study demonstrated that we obtained
vancomycin trough levels in the target therapeutic range early during the course of
therapy and that obtaining a higher
vancomycin AUC/MIC (in this case, >373) within 96 h was associated with reduced mortality. The MIC test method has a significant impact on
vancomycin AUC/MIC estimation. Clinicians should be aware that the current target AUC/MIC of ≥ 400 was derived using the reference BMD method, so adjustments to this target need to be made when calculating AUC/MIC ratio using other MIC testing methods.