The effect of the addition of lignocaine on propofol emulsion stability

The stability of propofol emulsion following the addition of various amounts of lignocaine solution was investigated. The investigations used were macroscopic and microscopic observations and electroacoustic determination of both droplet size and zeta potential. Evidence of emulsion instability was present following the addition of even small amounts of lignocaine. Resultant changes are unlikely to be clinically important following the addition of less than 20 mg of lignocaine to 200 mg of propofol (20 ml of propofol emulsion). It is recommended, however, that anaesthetists consider the possibility of destabilisation of propofol emulsion when adding larger doses of lignocaine, or when there is a delay between formulation and administration of the propofol-lignocaine mixtures.