The pharmacokinetics of epidural ropivacaine in infants and young children

The pharmacokinetic variables of ropivacaine were characterized after epidural bolus injection in pediatric patients. The subjects, 7 infants (aged 3-11 mo) and 11 young children (aged 12-48 mo), received 1.7 mg/kg of ropivacaine via a lumbar epidural catheter. Total plasma concentrations of ropivacaine measured over 24 h were assayed by high-pressure liquid chromatography, and pharmacokinetic modeling was performed by Nonlinear Mixed Effects Modeling analysis. The median peak venous plasma concentrations (C-max) in infants and young children were 620 mug/L (interquartile range [IQR], 550-725 mug/L) and 640 mug/L (IQR, 540-750 mug/L), respectively. The median times to maximum plasma ropivacaine concentration (T-max) were 60 min (IQR, 60-120 min) in infants and 60 min (IQR, 30-90 min) in young children. There were no statistical differences between median values of C-max and T-max between infants and young children. The calculated clearance (CL) in infants was 4.26 mL.min(-1)-.kg(-1) (9% coefficient of variation), and in young children it was 6.15 mL. min-(1).kg(-1) (11% coefficient of variation). The CL for infants was significantly less than the CL for young children (P < 0.01). The volume of distribution was estimated to be 2370 mL/kg (9% coefficient of variation) for both young children and infants. No systemic toxicity was observed in either group.