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
NAQVI SH, REICHLEY RM. Vancomycin Pharmacokinetics-Reply. Am J Dis Child. 1986;140(11):1097. doi:10.1001/archpedi.1986.02140250022016
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