This in turn is dependent on the size and number of oil droplets resulting from the injection.
In a propofol emulsion with the contents noted above (10% fat emulsion), oil droplet size is a significant factor.
Soybean oil holds the bulk of the propofol in a medium that can be stabilized and dispersed; lecithin serves as an emulsifier to stabilize the small propofol–soybean oil droplets in aqueous dispersion, and glycerol maintains the formulation isotonic with blood.34 The p H of the emulsion is adjusted with the base, sodium hydroxide, to around 7.0–8.5 for optimal emulsion stability.
In such a formulation, propofol is highly concentrated in the emulsified oil droplets (defined as the discontinuous phase), with only small quantities in the aqueous phase (Upon administration of a propofol-containing emulsion, propofol diffuses across the droplet interface and passes into the bloodstream.
The 1% formulation without ethanol was less painful upon injection.
Major factors that govern this process for propofol or any lipophilic drug are the drug concentration gradient, the partition coefficient, the drug diffusivity in both phases, and the interfacial area of the drug-containing oil droplets.35 Therefore, similar to any drug releasing particle, emulsions slow the availability of free drug as compared with drugs administered in solutions in which they are molecularly dissolved.
The total interfacial surface area is a highly important factor in the rate of drug release from a drug-containing droplet.
Propofol is a unique compound compared to the other intravenous anesthetics.
It is a simple phenol substituted with two isopropyl groups in each of the positions adjacent to the hydroxyl group, the ortho positions (fig. In its pure form at room temperature, it is an oil with a slightly yellowish color, but it freezes at only 19°C.