Fig. 3. Results of a previous study in rats in which thiopental was given as bolus injection (  top graph ; coefficient of variation = 31%) or as target-controlled infusions (TCIs) (  four lower graphs ). The  middle two graphs are a prospective result (coefficient of variation = 11%) obtained with the TCI programmed using the pharmacokinetics derived from the bolus injection study (  top graph ). The lower two graphs are a prospective result (coefficient of variation = 18%) obtained with the TCI programmed using the pharmacokinetics derived from the first TCI study (  i.e. , a refinement of the first TCI model, based on pharmacokinetic analysis of the  middle two graphs ). The  dotted line shows the target concentrations for the TCI administrations. The variability observed with target-controlled drug delivery is less than that after bolus injection, as predicted by the formal mathematical analysis and the simulations.