Haemolysis after etomidate: comparison of propylene glycol and lipid formulations

We sought to determine if the solvent in the formulation of etomidate is responsible for haemolysis in patients. In a randomized, prospective, double-blind study of 49 patients undergoing otolaryngological surgery, patients received etomidate dissolved in propylene glycol or in lipid emulsion. Concentrations of free haemoglobin and haptoglobin were measured before and for up to 360 min after injection of etomidate. Free haemoglobin concentrations increased by 216.8 mg litre(-1) in patients who received the propylene glycol formulation and by 11.8 mg litre(-1) in the lipid emulsion group (P less than or equal to 0.0004). Correspondingly, reductions in haptoglobin concentrations were significantly greater in the propylene glycol group (P less than or equal to 0.002). We conclude that with respect to haemolysis, lipid emulsion is superior to propylene glycol as a solvent for etomidate.