Fig. 1. Illustrative examples comparing linear ( right ) and nonlinear ( left ) approaches to pharmacokinetic modeling of thiopental. Log-linear R-thiopental serum concentration–time curves for two patients, where time 0 is time of commencement of thiopental infusion. ▪ Indicates observed R-thiopental serum concentration values. − Indicates the model fitted to the serum concentration values.