The original formulation of Etomidate injection contains propylene glycol as a solvent contributing to a high incidence of pain during IV injection and occasional venous irritation.
The newer lipid emulsion formulation is devoid of pain on injection and venous complications such as reddening, swelling, induration; as well as allergic reactions, whereas the incidence of myoclonus remains unchanged. The incidence of haemolysis is also less with lipid formulation.
However, the pharmacodynamic properties are the same. Administration through the oral mucosa results in direct systemic absorption while bypassing hepatic metabolism.
Etomidate injection is commercially available as a single isomer [R(+) isomer]. However etomidate is optically active and exists in two mirror-image enantiomeric forms R(+) and S(-) isomer.
The anaesthetic effect of etomidate injection resides pre dominantly in the more potent R(+) isomer.