An Evaluation of Using Population Pharmacokinetic Models to Estimate Pharmacodynamic Parameters for Propofol and Bispectral Index in Children

Background: To study propofol pharmacodynamics in a clinical setting a pharmacokinetic model must be used to predict drug plasma concentrations. Some investigators use a population pharmacokinetic model from existing literature and minimize the pharmacodynamic objective function. The purpose of the study was to determine whether this method selects the best-performing pharmacokinetic model in a set and provides accurate estimates of pharmacodynamic parameters in models for bispectral index in children after propofol administration. Methods: Twenty-eight children classified as American Society of Anesthesiologists physical status 1 who were given general anesthesia for dental treatment were studied. Anesthesia was given using target-controlled infusion of propofol based on the Kataria model. Propofol target plasma concentration was 7 mu g/ml for 15 min, followed by 1 mu g/ml for 15 min or until signs of awakening, followed by 5 mu g/ml for 15 min. Venous blood samples were taken 1, 2, 5, 10, and 15 min after each change in target. A classic pharmacokinetic-pharmacodynamic model was estimated, and the methodology of other studies was duplicated using pharmacokinetic models from the literature and (re-)estimating the pharmacodynamic models. Results: There is no clear relationship between pharmacokinetic precision and the pharmacodynamic objective function. Low pharmacodynamic objective function values are not associated with accurate estimation of the pharmacodynamic parameters when the pharmacokinetic model is taken from other sources. Conclusion: Minimization of the pharmacodynamic objective function does not select the most accurate pharmacokinetic model. Using population pharmacokinetic models from the literature instead of the 'true' pharmacokinetic model can lead to better predictions of bispectral index while incorrectly estimating the pharmacodynamic parameters.