Vancomycin protein binding in patients with infections caused by Staphylococcus aureus

The protein binding of vancomycin has been reported to range from less than 10 percent to 82 percent. We examined the binding of vancomycin in 34 patients (14 intravenous drug abusers, 10 burn patients, and 10 control patients) with Staphylococcus aureus infections. Blood samples were collected serially over an 8- or 12-hour dosing interval following a one-hour infusion. In vitro studies were also performed using albumin solutions of varying concentrations. Binding characteristics were determined through ultrafiltration with vancomycin concentrations analyzed for fluorescence polarization immunoassay. The unbound fraction of vancomycin ranged from 0.41 to 0.77 with a mean of 0.54 +/- 0.08. Unbound fractions was significantly correlated with serum albumin concentration (r = -0.344, p less than 0.046) and renal clearance (r = 0.394, p less than 0.021) but not with total body clearance or volume of distribution. In vitro data also showed an association between albumin concentration and unbound fraction (r = -0.94, p less than 0.017). Although vancomycin protein binding changes with serum albumin, this finding may have limited clinical significance.