Vancomycin Pharmacokinetics-Reply

Abstract

In Reply .—Dr Murray is correct in pointing out that the volume of distribution (Vd) and clearance (Cl) will be underestimated using a one-compartment model in which the apparent Vd is calculated from the linear extrapolation of phase to end of infusion. 1 We calculated the Vd based on the measured peak level of serum vancomycin corrected for the fraction eliminated during the one-hour infusion. The difference in the two calculations was minor (Figure). After an accurately timed one-hour infusion, the mean actual peak was less than 2 μg/L greater than the mean β-extrapolated peak in seven patients less than 41 weeks after conception. The Vd calculated from the measured peak was 0.43 L/kg, and the Cl was 64.07 mL/kg/h. The Vd calculated from the β-extrapolated peak was 0.45 L/kg, and the Cl was 67.05 mL/kg/h. There was far more variability observed in the β-extrapolated peak, indicating a greater potential