OBJECTIVES: To evaluate the relationship between vancomycin trough concentration and the clinical outcome in hospitalized patients with ORSA bacteremia, and to assess the relationship between vancomycin trough concentration and nephrotoxicity. METHODS: Adult patients admitted to National Cheng-Kung University Hospital during January 20, 2006 and July 31, 2006 and treated with vancomycin for ORSA bacteremia were eligible for this prospective observational study. On the fourth day after vancomycin use, vancomycin concentration was monitored and blood culture was repeated. Regular biochemistry and blood test on day 4, 7, 11, 14, daily highest temperatue and other associated data were collected. The primary endpoints are the clinical outcome and the change of serum creatinine concentration. RESULTS: Nineteen patients were enrolled during this period. On day 4, trough concentration of vancomycin was associated with the rate of defervescence. The afebrile rate were 85.7% and 33.3% among patients with trough level of above and below 15 μg/mL, respectively (P = 0.05). For the ratio of vancomycin trough concentration to MIC, patients with ratio greater than 10 had a trend of a higher defervescence rate in comparison with those with ratio less than 10 (77.8% vs. 30%, P = 0.07). In addition, nephrotoxicity was found in five patients, but the mean trough concentrations were not significantly different between the nephrotoxic and non-nephrotoxic groups.  CONCLUSIONS:    The result of the study shows that higher serum vancomycin trough concentration is associated with the defervescence rate on day 4 when vancomycin is used to treat ORSA bacteremia. Besides, under the condition of regular therapeutic drug monitoring, the nephrotoxicity during vancomycin therapy doesn’t seem to be associated with trough concentration, but it needs studies with large sample size to evaluate.