Influence of different fat emulsion-based intravenous formulations on the pharmacokinetics and pharmacodynamics of propofol

Purpose. The influence of different intravenous formulations on the pharmacokinetics and pharmacodynamics of propofol was investigated using the effect on the EEG (11.5-30 Hz) as pharmacodynamic endpoint. Methods. Propofol was administered as an intravenous bolus infusion (30 mg/kg in 5 min) or as a continuous infusion (150 mg/kg in 5 hours) in chronically instrumented male rats. Propofol was formulated as a 1% emulsion in an Intralipid 10%(R)-like fat emulsion (Diprivan-10(R), D) or as a 1%- or 6% emulsion in Lipofundin(R) MCT/LCT-10% (P1% and P6%, respectively). EEG was recorded continuously and arterial blood samples were collected serially for the determination of propofol concentrations using HPLC. Results. Following bolus infusion, the pharmacokinetics of the various propofol emulsions could adequately be described by a two-compartmental mental pharmacokinetic model. The average values for clearance (CI), volume of distribution at steady-state (V-d,V-ss) and terminal half-life (t(1/2,lambda 2)) were 107 +/- 4 ml/min/kg, 1.38 +/- 0.06 l/kg and 16 +/- 1 min, respectively (mean +/- S.E., n = 22). No significant differences were observed between the three propofol formulations. After continuous infusion these values were 112 +/- 11 ml/min/kg, 5.19 +/- 0.41 l/kg and 45 +/- 3 min, respectively (mean +/- S.E., n = 20) with again no statistically significant differences between the three propofol formulations. Comparison between the bolus-and the continuous infusion revealed a statistically significant difference for both V-d,V-ss and t(1/2,lambda 2) (p < 0.05). whereas Cl remained unchanged. In all treatment groups infusion of propofol resulted in a burst-suppression type of EEG. A profound hysteresis loop was observed between blood concentrations and EEG effect for all formulations. The hysteresis was minimized by a semiparametric method and resulted in a biphasic concentration-effect relationship of propofol that was described non-parametrically. For P6% a larger rate constant onset of drug effect (t(1/2,keo)) was observed compared to the other propofol formulations (p < 0.05). Conclusions. The pharmacokinetics and pharmacodynamics of propofol are not affected by to a large extent the type of emulsion nor by the concentration of propofol in the intravenous formulation.