Prediction of serum gentamicin concentrations in patients undergoing hemodialysis

The predictability of a one-compartment pharmacokinetic model for estimating serum gentamicin concentrations in patients undergoing hemodialysis was studied. Nine hemodialysis patients with gram-negative bacillary infections requiring aminoglycoside therapy and with creatinine clearances of less than 1 ml/min were studied. A series of blood samples was assayed by radioimmunoassay to determine serum concentrations after an initial 1.5- to 2.0-mg/kg i.v. dose and throughout the dialysis period. These data were used to predict post-dialysis serum concentrations and post-dialysis doses needed to achieve therapeutic concentrations. The mean apparent volume of distribution for gentamicin was 0.26 +/- 0.06 liter/kg. The mean gentamicin half-life was 31.5 hours before dialysis and 7.6 hours during dialysis. No significant differences were found between predicted and measured peak gentamicin serum concentrations after dialysis; nor were there significant differences for peak serum concentrations obtained with a post-dialysis gentamicin dose (p less than 0.001). Neither the peaks predicted based on the individual patient's pharmacokinetic values nor those based on the average of the patients' pharmcokinetic values were statistically different from measured. The kinetic model developed can be used to determine gentamicin dosing for hemodialysis patients and to determine an average elimination rate constant for a given dialysis apparatus.