Etomidate is a carboxylated imidazole intended for the induction of general anesthesia. It is marketed as the more potent R (+) isomer. It is believed to exert its anesthetic effect via positive modulation of the GABAA receptor.44 It is not water soluble and is available in the United States as a 2-mg/mL solution containing 35% v/v propylene glycol and in Europe as a soybean oil and medium-chain triglycerides formulation.4546 The propylene glycol has been associated with moderate-to-severe pain on injection and irritation of the vascular tissue.46 A high incidence of skeletal muscle movements were noted in about 32% of patients following etomidate injection. Case reports of seizures are also found in the literature.47 Administration of etomidate has little effect on cardiac output, peripheral, or pulmonary circulation. Studies have found that etomidate, even after a single dose, reduces plasma cortisol and aldosterone levels. Etomidate should not be used in patients with severe sepsis as the adrenal insufficiency has been shown to increase the risk of death in these patients.48 This is probably a result of the inhibition of the 11 3-hydroxylase enzyme. Etomidate should only be used for induction of anesthesia when the cardiac benefits outweigh the risks associated with adrenal insufficiency.
Etomidate is quickly distributed throughout most organs in the body after intravenous administration and the tissue concentrations equal and sometimes exceed the plasma concentrations. The lipid solubility of the drug allows it to rapidly penetrate into the brain with peak concentrations occurring within 1 minute of administration. Etomidate is rapidly metabolized in the plasma and liver via esterases. About 75% of the drug is eliminated in the urine as the inactive ester hydrolyzed carboxylic acid.49
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