The relationship between trough concentration of vancomycin and effect on methicillin-resistant Staphylococcus aureus in critically ill patients

Objectives. The incidence of methicillin-resistant Staphylococcus aureus (MRSA) infections in intensive care units in Malaysia is significant. Invasive MRSA infections are commonly treated with vancomycin. In clinical practice, the serum vancomycin trough concentration is used as a surrogate marker of vancomycin efficacy. A low concentration of vancomycin may result in less effective therapy and increase the risk of bacterial resistance. We evaluated the relationship between the resolution of MRSA infections and trough concentrations of vancomycin. Methods. A total of 76 patients admitted between January 2005 and February 2011 were included in the study. Serum vancomycin trough concentration data were collected from the microbiology records. The clinical response was evaluated on the basis of clinical notes and culture test results. Results. A total of 262 appropriate trough concentration data was included, with a median of 3 trough concentrations per patient. Fifty-four patients responded to vancomycin therapy. The initial trough concentration did not differ between responders and non-responders (p=0.135), but the corrected trough concentration was higher among responders than among non-responders (11.64 +/- 1.50 mg/l and 9.25 +/- 1.59 mg/l, respectively; p=0.036). The average total daily dose of vancomycin was significantly higher among the responders (p=0.008). Conclusion. In this critically ill population, a vancomycin dose of 15 mg/kg/day was found sufficient to produce optimal trough concentrations to eradicate the MRSA infection. This study demonstrated the significant relationship between response to treatment of MRSA infection and serum vancomycin trough concentrations.