Pharmacokinetics of S-ketamine during prolonged sedation at the pediatric intensive care unit.

Background: S-ketamine is the S(+)-enantiomer of the racemic mixture ketamine, an anesthetic drug providing both sedation and analgesia. In clinical practice, significant interpatient variability in drug effect of S-ketamine is observed during long-term sedation.

Aims: The aim of this study was to evaluate the pharmacokinetic variability of S-ketamine in children aged 0-18 years during long-term sedation. Twenty-five children (median age: 0.42 years, range: 0.02-12.5) received continuous intravenous administrations of 0.3-3.6 mg/kg/h S-ketamine for sedation during mechanical ventilation. Infusion rates were adjusted to the desired level of sedation and analgesia based on the COMFORT-B score and Visual Analog Scale. Blood samples were drawn once daily at random time-points, and at 1 and 4 hours after discontinuation of S-ketamine infusion. Time profiles of plasma concentrations of S-ketamine and active metabolite S-norketamine were analyzed using nonlinear mixed-effects modeling software. Clearance and volume of distribution were allometrically scaled using the ¾ power model.

Results: A total of 86 blood samples were collected. A 2-compartment and 1-compartment model adequately described the PK of S-ketamine and S-norketamine, respectively. The typical parameter estimates for clearance and central and peripheral volumes of distribution were: CL =112 L/h/70 kg, V1 =7.7 L/70 kg, V2 =545L/70 kg, Q =196 L/h/70 kg, and CL =53 L/h/70 kg. Interpatient variability of CL and CL was considerable with values of 40% and 104%, respectively, leading to marked variability in steady-state plasma concentrations.

Conclusion: Substantial interpatient variability in pharmacokinetics in children complicates the development of adequate dosage regimen for continuous sedation.