Thoughts on "Population pharmacokinetics and relationship between demographic and clinical variables and pharmacokinetics of gentamicin in neonates"

Two nomograms for determining extended-dosing intervals for gentamicin in neonates

PURPOSE

The development of two nomograms to predict dosing intervals for gentamicin in neonates based on one gentamicin concentration is described.

METHODS

Pooled data from three retrospective studies on neonates age seven days or younger were used to create nomograms that would predict dosing intervals for gentamicin. The population volume of distribution (0.45 L/kg) and a determined half-life were used to create nomogram cutoff concentrations that could select a dosing interval for neonates to achieve steady-state trough concentrations of < or =0.5 or < or =1 mg/L. A dose of 4 mg/kg was used to simulate concentration-versus-time profiles for included neonates based on their individual pharmacokinetic data. Predicted concentrations from hours 6 to 22, at one-hour intervals, for each neonate were compared against the nomograms and evaluated for the number of correct interval predictions. The nomograms were considered to have failed at any time point where they indicated an interval that would not have achieved the desired trough concentration of < or =0.5 or < or =1 mg/L or if the interval chosen was longer than necessary.

RESULTS

The 0.5- and 1-mg/L nomograms predicted correct dosing intervals for 81-92% of neonates for postinfusion hours between 15 to 21 and 86-93% for postinfusion hours of 13 and 21, respectively. Accuracy of the nomograms to predict correct dosing intervals improved as the postinfusion time before the next concentration measurement increased.

CONCLUSION

Using the two nomograms may help predict the correct extended-dosing intervals of gentamicin administration for neonates. Prospective evaluation and validation of the nomograms may be necessary for their wider use as a clinical tool.

Population pharmacokinetics of ciprofloxacin in pediatric and adolescent patients with acute infections

The aim of the present study was to characterize the population pharmacokinetics of ciprofloxacin in patients with and without cystic fibrosis ranging in age from 1 day to 24 years and to propose a limited sampling strategy to estimate individual pharmacokinetic parameters. Patients were divided into four groups according to the treatment schedule. They received ciprofloxacin by intravenous infusion (30 min) or by the oral route. The number of samples collected from each patient ranged from 1 to 12. The population parameters were computed for an initial group of 37 patients. The data were analyzed by nonlinear mixed-effect modeling by use of a two-compartment structural model. The interindividual variability in clearance (CL) was partially explained by a dependence on age and the patient's clinical status. In addition, a significant relationship was found between weight and the initial volume of distribution. Eighteen additional patients were used for model validation and evaluation of limited sampling strategies. When ciprofloxacin was administered intravenously, sampling at a single point (12 h after the start of infusion) allowed the precise and accurate estimation of CL and the elimination half-life, as well as the ciprofloxacin concentration at the end of the infusion. It should be noted that to take into account the presence of a lag time after oral administration, a schedule based on two sampling times of 1 and 12 h is needed. The results of this study combine relationships between ciprofloxacin pharmacokinetic parameters and patient covariates that may be useful for dose adjustment and a convenient sampling procedure that can be used for further studies.