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November 1986

Vancomycin Pharmacokinetics-Reply

Author Affiliations

Department of Pediatrics/Adolescent Medicine St Louis University School of Medicine
Pharmacy Department Cardinal Glennon Children's Hospital 1465 S Grand Blvd St Louis, MO 63104

Am J Dis Child. 1986;140(11):1097. doi:10.1001/archpedi.1986.02140250022016

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