Etomidate

Etomidate is a short acting intravenous anaesthetic agent used for the induction of general anaesthesia and for sedation for short procedures such as reduction of dislocated joints and cardioversion. It was discovered at Janssen Pharmaceutica in 1964.

Drug class
Etomidate, a hypnotic is a carboxylated imidazole derivative. Etomidate has anesthetic and amnestic properties, but has no analgesic properties.

Uses
Etomidate is commonly used in the emergency setting as part of a rapid sequence induction to induce anesthesia or for conscious sedation. It is often used in this setting since it has a rapid onset of action and a low cardiovascular risk profile, and therefore is less likely to cause a significant drop in blood pressure than other induction agents.

In the operating room with a stable patient, anesthesiologists may choose an alternative induction agent, such as propofol, thiopental or methohexital. (see Side effects below).

At the typical dose, anesthesia is induced for about 5–10 minutes even though the half-life of drug metabolism is approximately 75 minutes. This is because etomidate is redistributed from the plasma to other tissues.

Dosage
The anaesthetic induction dose for adult humans is 0.3 mg/kg intravenously, with a typical dose ranging from 20-40 mg. In common with all induction agents, etomidate causes loss of consciousness after one arm-brain circulation time. In very brief procedures such as cardioversion, a 10 mg dose may be used which may be repeated for effect.

Metabolism
Etomidate is highly protein bound in blood plasma and is metabolised by hepatic and plasma esterases to inactive products. It exhibits a bi-exponential decline, with a redistribution half-life of 2–5 minutes and an elimination half-life of 68–75 minutes.

Side effects
The use of etomidate infusions for sedation of critically ill patients in intensive care units has been associated with increased mortality, which is due to suppression of steroid synthesis (both glucocorticoids and mineralocorticoids) in the adrenal cortex. This effect has been demonstrated after a single dose, and lasts about 24 hours. There is no evidence that a single induction dose of etomidate has any effect on morbidity or mortality. However, some sources advise giving a prophylactic dose of steroids (e.g. hydrocortisone) if etomidate is used.

Seizure-like activity is occasionally seen with anesthetic induction. In the absence of concurrent EEG monitoring, it is difficult to ascribe this to cortical activity. Myoclonic movement originating at the spinal cord level is often a likely mechanism. Excitatory phenomena, and epileptiform movements and EEG activity may be observed during induction. Etomidate consistently increases the amplitude of somatosensory evoked potentials (in contrast to most anaesthetic agents).

Etomidate in the propylene glycol formulation may produce pain on injection, a side effect which is less likely with the lipid formulation.

There is a 30-fold difference between the effective dose and the lethal dose of etomidate, making it an extremely safe agent.

Formulation
Etomidate is usually presented as a clear colourless solution for injection containing 2 mg/ml of etomidate in an aqueous solution of 35% propylene glycol, although a lipid emulsion preparation (of equivalent strength) has also been introduced. Etomidate is presented as a racemic mixture, but only the D-isomer has pharmacological activity.

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