Effect of altered volume of distribution on aminoglycoside levels in patients in surgical intensive care
P. W. Niemiec Jr, M. D. Allo and C. F. Miller
The apparent volume of distribution (Vd) of aminoglycosides was found to be
increased in 100 patients in a surgical intensive care unit who had
gram-negative pneumonia or intraabdominal sepsis and acute physiologic
scores greater than 12. Following loading or maintenance doses, carefully
timed blood samples were collected for measurements of serum concentrations
by fluorescence polarization immunoassay. The Vd, determined by linear
regression analysis of a one-compartment model using the Sawchuk-Zaske
method, was 0.34 +/- 0.121 L/kg and was larger than the normal Vd of 0.20
to 0.25 L/kg, suggesting a 36% to 70% increase in extracellular fluid
volume. Since there is a predictable increase in aminoglycoside Vd in the
septic surgical patient, a proportionately larger aminoglycoside dosage is
required initially to achieve desirable peak serum levels. Close monitoring
of blood levels during maintenance dosing is suggested since dynamic
changes in renal function and aminoglycoside Vd occur in the critically
ill.
