LAUSR

Learning Objectives: For critically ill adults receiving empiric vancomycin, the duration of negative cultures after which vancomycin may be discontinued without risking subsequent growth of Staphylococcus aureus in culture remains unknown. We hypothesized that if cultures did not demonstrate growth of Staphylococcus aureus by 48 hours after the initiation of empiric vancomycin, those cultures would not subsequently demonstrate Staphylococcus aureus. Methods:We conducted an ancillary analysis using data from patients enrolled in the Isotonic Solutions and Major Adverse Renal Events Trial (SMART). In this cohort of all adult patients admitted to 5 intensive care units (ICUs) at a single, academic center, we collected data from the electronic health record on the time of Staphylococcus aureus identification in culture and the time to vancomycin discontinuation. Results: Of the 15,802 patient admissions in the SMART study, 6,553 (41.5%) received empiric vancomycin. Cultures demonstrated methicillin-resistant Staphylococcus aureus (MRSA) bacteremia during a total of 85 patient admissions and demonstrated MRSA pneumonia during 178 patient admissions. During episodes of bacteremia, Gram positive cocci were identified on Gram stain at a median of 21.3 [IQR 17–25.8] hours after cultures were obtained. The median time to Staphylococcus aureus identification was 45.5 [41.9–50.8] hours for bacteremia and 33.3 [24.6–44.1] hours for pneumonia. Among blood cultures that would ultimately grow Staphylococcus aureus, 61% resulted positive within 48 hours and 98% within 72 hours. Among respiratory cultures that would ultimately grow Staphylococcus aureus, 85% resulted positive within 48 hours and 97% within 72 hours. Conclusions: In this analysis of a large cohort of critically ill adults receiving empiric vancomycin, nearly 40% of patients whose blood cultures ultimately grew Staphylococcus aureus had negative blood cultures at 48 hours, but less than 3% had negative blood cultures at 72 hours. Future research should explore whether 72 hours with negative blood and respiratory cultures represents the optimal time at which to discontinue empiric vancomycin therapy.