Treatment of Methicillin-Resistant Staphylococcus Aureus with a Vancomycin Minimum Inhibitory Concentration of 2 mcg/mL

Abstract

Background Vancomycin has been considered the standard of therapy for infections caused by methicillin-resistant Staphylococcus aureus (MRSA) for decades. The aims of this study were to describe the clinical outcomes of patients with infections caused by MRSA with a vancomycin minimum inhibitory concentration (MIC) of 2 mcg/mL and determine whether achievement of a high vancomycin trough concentration affected outcomes. Methods A retrospective analysis was conducted on data from a single medical center from 2003 through 2007. The study included patients with a culture positive for MRSA with a vancomycin MIC of 2 mcg/mL who received vancomycin therapy. Treatment groups were determined by weighted average vancomycin trough concentration. Subjects were assigned to either the conventional (less than 15 mcg/mL) or high (15 mcg/mL or higher) trough group. Outcome measures included attainment of clinical cure, all-cause mortality, and occurrence of nephrotoxicity. Results Of the 79 patients included in the study, 50 (63.3%) attained clinical cure. Rate of clinical cure was similar between the conventional and high trough groups (64.7% vs 60.7%, P = 0.7). Treatment arms were similar in regard to all-cause mortality and other secondary endpoints. Patients demonstrating clinical response at 72 hours were significantly more likely to progress to clinical cure than those continuing to show signs of infection (77.8% vs 32.5, P < 0.001). Conclusions Use of vancomycin for the treatment of MRSA with a vancomycin MIC of 2 mcg/mL resulted in a low rate of clinical cure. Data from this study suggest that achieving higher vancomycin trough concentrations is not a sufficient strategy for enhancing efficacy in these challenging infections.