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Estimation of gentamicin clearance and volume of distribution in neonates and young children
Insights
Gentamicin dosing requires serum level monitoring for all ages, with adjustments based on age-related pharmacokinetic changes. A new nomogram aids in achieving target peak gentamicin concentrations in infants, ensuring safe trough levels.
Area of Science:
- Pharmacology
- Pediatric Medicine
- Clinical Pharmacy
Background:
- Gentamicin therapy necessitates careful dosing due to age-related pharmacokinetic variations.
- Accurate serum level monitoring is crucial for optimizing gentamicin efficacy and safety across all pediatric age groups.
Purpose of the Study:
- To analyze population pharmacokinetic data of gentamicin in infants and children.
- To develop a dosing nomogram for gentamicin therapy in pediatric patients.
- To improve the precision of gentamicin concentration predictions using Bayesian methods.
Main Methods:
- Population pharmacokinetic analysis using NONMEM software.
- Prospective forecasting of gentamicin concentrations with a Bayesian kinetic parameter estimation program.
- Development and validation of a simple nomogram for gentamicin dosing.
Main Results:
- Volume of distribution and clearance of gentamicin are significantly influenced by body weight in children.
- Renal function (creatinine concentrations) did not provide additional explanatory power for gentamicin pharmacokinetics.
- Trough gentamicin concentrations were more accurately predicted than peak concentrations with a single measurement; two measurements improved precision for both.
Conclusions:
- Gentamicin dosage adjustments are essential based on age-related pharmacokinetic changes, particularly volume of distribution and clearance related to body weight.
- A practical nomogram incorporating these findings can guide gentamicin dosing to achieve target peak concentrations while maintaining safe trough levels (<2 µg/ml) in infants.
- Serum level monitoring and Bayesian analysis enhance the precision of gentamicin dosing strategies in pediatric populations.
Abstract:
Gentamicin therapy should be guided by serum level monitoring in all age groups, dosage adjustments depending on age related changes in pharmacokinetics. Population data analysed from two centres (43 infants from Glasgow and 100 infants and children from Manchester) by the computer program NONMEM showed that volume of distribution was related to body weight by a proportionality factor that decreased from the region of 0.41-0.46 l/kg in children less than 3 months to 0.25-0.32 l/kg in older children, a value which merges with that accepted for adults (0.25 l/kg). In both young and older children, clearance was also found to be dependent on body weight. Renal function (creatinine concentrations) provided no further explanatory power. When these results were used prospectively to forecast gentamicin concentrations with a Bayesian kinetic parameter estimation program, trough concentrations were more precisely predicted than peaks when a single concentration measurement was used. In clinical practice, however, two concentration measurements are usually routinely available and these should lead to greater precision of both peak and trough predictions. These results have been incorporated into a simple nomogram which can be used to determine a dose of gentamicin which will achieve target peak concentrations in infants, assuming that troughs should not exceed 2 micrograms/ml.