Vancomycin AUC₂₄/MIC Ratio in Patients with Methicillin-Resistant Staphylococcus aureus Pneumonia

Background: Vancomycin is the treatment of choice for serious methicillin-resistant Staphylococcus aureus (MRSA) infections. The area under the concentration–time curve from 0 to 24 hr (AUC₂₄)/minimum inhibitory concentration (MIC) ratio was recently introduced as a parameter for assessing clinical outcome by S. aureus. This study was purposed to apply the vancomycin AUC₂₄/MIC in patients with MRSA pneumonia. Methods: Forty-seven patients with confirmed lower respiratory infection caused by MRSA during 2011 were enrolled. All patients were treated with vancomycin. Clinical characteristics and laboratory data were collected. AUC₂₄/MIC values were calculated as previously reported and patients were divided into two groups based on the bacteriologic response, which was eradicated or not, and an AUC₂₄/MIC value (above or below 400). Results: MRSA infections were eradicated in 39 patients but 8 patients had persistent MSRA infection in the following cultures. The mean AUC₂₄/MIC values and vancomycin concentrations were not statistically different between patients with and without MRSA eradication. All 13 patients with a vancomycin MIC of 2 mg/L had an AUC₂₄/MIC below 400. Conclusion: AUC₂₄/MIC might not be a reliable indicator for assessing treatment response of vancomycin in MRSA pneumonia. Relationship between vancomycin AUC₂₄/MIC and therapeutic outcome needs to undergo further studies, including sufficiently large sample size.