Effect of variables associated with intermittent gentamicin infusions on pharmacokinetic predictions
Armtistead, J.A.; Nahata, M.C.
Clinical Pharmacy 2(2): 153-156
1983
ISSN/ISBN: 0278-2677 PMID: 6883943 Document Number: 213566
Variables associated with intermittent gentamicin infusions that influence pharmacokinetic predictions were assessed. Phase 1 of this study measured the total volume of fluid in the most commonly prepared dose (80 mg of gentamicin in 100 ml of 5% dextrose injection). To represent prepared doses, 2 ml of 0.9% NaCl was added to 100 containers of 5% dextrose injection to simulate a 2 ml volume of gentamicin 40 mg/ml. Then, the piggybacks were drained and their volumes measured. In phase 2, fluid lost through priming the administration tubing was measured for 50 doses. In phase 3, 50 minibags and administration sets were collected from patients' rooms after the dose infusions; the volume of fluid remaining in the infusion system (representing the unadministered amount) was measured. In phase 4, the starting and completion times for 50 doses of gentamicin were observed. In phase 5, 25 patients receiving gentamicin were studied to contrast predicted and actual peak and trough serum concentrations. Standard pharmacokinetic predictions were based on the assumed doses and infusion times, while corrected predictions used the actual doses and infusion times. Phase 1 (100 minibags) showed a consistent overfill of piggyback diluent (9.5 .+-. 0.9%). Phase 2 and 3 showed that a substantial volume of fluid was not administered to the patient, causing a 7.2 .+-. 1.4% decrease in the dose administered. Phase 4 showed a range of infusion durations from 5 to 110 min. The starting times of the infusions ranged from 50 min before to 200 min after the scheduled times. The standard prediction mean peak and trough values were 22.7% and 18.2% higher than the actual laboratory values, respectively, while the corrected prediction means were 16.7% and 4.4% higher. Knowledge of the variables associated with intermittent gentamicin infusions can enhance the accuracy of pharmacokinetic predictions.