Emulsion formulation reduces propofol's dose requirements and enhances safety.

Background: Propofol, a highly lipophilic anesthetic, is formulated in a lipid emulsion for intravenous use. Propofol has brisk onset and offset of effect after rapid administration and retains rapid offset characteristics after long-term administration. The authors tried to determine whether the emulsion vehicle is requisite for propofol's evanescent effect-time profile.
Methods: The time course of sedation and electroencephalographic (EEG) effect after propofol administration was measured in three studies in rats instrumented. In study 1, propofol was infused in either emulsion or lipid-free vehicle (n = 12), in a repeated measures cross-over design. In study 2, propofol in lipid-free vehicle was infused with or without simultaneous infusion of drug-free lipid emulsion (n = 6) in a repeated measures cross-over design. In study 3, propofol was infused in either emulsion (n = 5) or lipid-free vehicle (n = 5) to EEG burst suppression.
Results: In study 1, relative to the emulsion formulation, propofol administered at equivalent doses in lipid-free vehicle resulted in a longer time to effect onset (1.4 +/- 0.2 vs. 0.5 +/- 0.1 min, EEG) and a trend for delayed anesthetic recovery (26.8 +/- 9.4 vs. 17 +/- 3.5 min, EEG; 26.1 +/- 8.8 vs. 16.8 +/- 3.3 min, sleep). In study 2, coadministration of drug-free emulsion with propofol did not alter the time course of effect. In study 3, more than twice the dose of propofol was required to achieve EEG burst suppression with the lipid-free formulation. Two animals died after administration of propofol to EEG burst suppression with the lipid-free formulation; no deaths occurred in the emulsion group.
Conclusion: The incorporation of propofol in emulsion reduces dose requirements and produces rapid onset and recovery of anesthetic effect.