- Induction of anaesthesia with a dose of 0.3mg/kg
- Maintenance of anaesthesia via infusion, although this is associated with an increased mortality in ICU patients
- Treatment of Cushing's disease
Etomidate
Etomidate
- Etomidate is a carboxylated imidazole ester derivative
- Its use in the UK has largely ceased due to undesirable pharmacodynamic properties (BJA, 2025)
- Only the R(+) enantiomer exhibits anaesthetic properties; the S(-) ennatiomer is 10x less potent
- It presents as:
- 20mg of R-etomidate in 10ml of 35% propylene glycol
- ± as a lipid emulsion to reduce pain on injection
- This gives a 0.2% solution with a pKa of 4.1
- Weak base
- Highly lipid soluble
- Molecular weight of 342.36g/mol
Absorption
- Onset within 60s and peak effect at 1 minute
Distribution
- 75% protein bound
- Volume of distribution 3 L/kg
Metabolism
- Hepatic metabolism with a hepatic extraction ratio of 0.5
- Non-specific hepatic esterases
- Hydrolysed to ethyl-alcohol and carboxylic acid metabolites
- Action terminated mostly by rapid distribution into the tissues
Excretion
- Elimination half life 3 - 5hrs
- Mostly renally (85%) excreted, although some is excreted in bile (13%)
- Clearance is reduced in presence of 67% N2O
Respiratory
- Minimal respiratory depression with transient coughing/hiccoughs
- Slight depression of ventilatory response to CO2
Cardiovascular
- Very stable cardiovascular profile
- Doesn't suppress the baroreceptor reflex or sympathetic nervous system, which leaves myocardial oxygen supply/consumption, contractility and BP unchanged
- Slight reduction in PVR
Neurological
- Produces hypnosis via action on β2 and β3 subunits of the GABAA receptor
- Does not produce analgesia
- Reduces CBF, CMRO2
- Reduces IOP at induction dose
- Excitatory phenomena
- Causes excitatory/myoclonic movements and hypertonus that is not epileptiform
- Myoclonus occurs in up to a third of patients
- 20% demonstrate generalised epileptiform activity on EEG associated with δ-wave activity and grand mal seizure
Gastrointestinal
- Is emetogenic, increasing rate of N&V
- May precipitate porphyric crisis
Metabolic
- Dose-dependent, reversible inhibition of 11-β-hydroxylase causes reduced adrenocortical function
- Causes reduced cortisol and aldosterone synthesis for 24hrs post-administration
- It increases mortality when used as an infusion to sedate septic patients on ICU
- I.e. the situation in which it has the best CV profile are those in which the consequences of steroid inhibition are most detrimental
Haematological
- Anti-platelet activity
- May cause venous thrombosis
Other
- Pain on injection (25-50%) reduced by use of lidocaine or lipuro formations