Prediction of gentamicin serum levels using a one-compartment open linear pharmacokinetic model

The accuracy of predicting serum gentamicin levels based on a one-compartment open linear pharmacokinetic model was studied. Twenty-two patients accounted for 59 serum gentamicin levels which were measured by microbiologic assay and compared with predicted serum levels determined by pharmacokinetic calculation. Seventeen serum levels were collected at peak times, 15 at trough time and 27 at times between peak and trough. Forty-nine of the levels were obtained from patients with impaired renal function. Predicated gentamicin levels correlated well with measured serum levels (r = 0.85, p less than 0.001). Of the measured levels, 56% were within +/- 1 microgram/ml of the predicted levels. Of 49 levels collected from patients with impaired renal function, 59% were within +/- 1 microgram/ml of the predicted level. In 13 patients from whom multiple serum gentamicin levels were collected and predictions based on half-life or elimination rate obtained by fitting the first level, 83% of the measured levels were within +/- 1 microgram/ml of the predicted level. The one-compartment open linear pharmacokinetic calculations can be used to adequately predict serum gentamicin levels. In patients with changing or diminished renal function, pharmacokinetic predictions may not be accurate, and actual serum level determinations may be needed to monitor gentamicin therapy.