Population Pharmacodynamic Modeling without Plasma Concentrations of Rocuronium in Children

Using the pharmacodynamic model without plasma concentrations described by Bragg et al, an individual approach resulted in highly variable parameters for rocuronium. Using a population approach of the model, the time course of the effect of an IV bolus dose of 400, 600, and 800 microg/kg of rocuronium was studied. Response was measured by accelerometry (TOF-Guard) in 45 low-risk surgical children, ages 2 to 14 years, who were receiving general anesthesia with isoflurane. Using a Bayesian approach and the software P-PHARM, response (the first twitch of the TOF) was modeled. The apparent rate constant of elimination, the rate constant for equilibrium between plasma and the effect compartment, the sigmoidicity factor of the relationship between drug concentration in the effect compartment and the effect, and the infusion rate that produces 50% of the effect at steady state were obtained. Population and individual post hoc parameters were similar among groups and variability was reduced.