1. Clinical Overview
Etomidate is a potent, ultra-short-acting, non-barbiturate intravenous hypnotic agent used for the induction of general anesthesia. It is chemically unrelated to other intravenous anesthetics. It is characterized by rapid onset, short duration of action, minimal cardiovascular depression, and minimal histamine release, making it particularly valuable in hemodynamically unstable patients, the elderly, and those with significant cardiac disease. Its primary drawback is the suppression of adrenal steroidogenesis, which can be clinically significant with prolonged infusion.
| Onset | Duration | Bioavailability |
|---|---|---|
| Within 30-60 seconds after intravenous injection. | Approximately 3-5 minutes for a single induction dose. | 100% (Intravenous administration). |
2. Mechanism of Action
Etomidate acts as a positive allosteric modulator of the gamma-aminobutyric acid type A (GABA-A) receptor, the primary inhibitory neurotransmitter receptor in the central nervous system. It enhances GABA-mediated chloride ion influx into neurons, leading to hyperpolarization of the postsynaptic membrane and inhibition of neuronal firing, resulting in hypnosis and loss of consciousness.
3. Indications & Uses
- Induction of general anesthesia
- Rapid sequence intubation (RSI) in hemodynamically unstable patients
4. Dosage & Administration
Adult Dosage: Induction: 0.2 to 0.6 mg/kg (typically 0.3 mg/kg) IV over 30-60 seconds. Average dose: 20 mg for a 70 kg adult.
Administration: For IV use only. Must be diluted or administered into a large vein (e.g., antecubital) to minimize pain and thrombophlebitis. Administer as a slow IV injection over 30-60 seconds. Pre-treatment with lidocaine or an opioid (e.g., fentanyl) can reduce injection pain and myoclonus. Always have resuscitation equipment and personnel trained in airway management present.
5. Side Effects
Common side effects may include:
- Pain on injection (up to 80% of patients)
- Transient myoclonus or involuntary muscle movements (30-60%)
- Nausea and vomiting (post-operative)
- Hiccups
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Fentanyl, other opioids | Enhanced respiratory depression and CNS depression. | Major |
| Benzodiazepines (Midazolam, Diazepam) | Synergistic sedative and hypnotic effect. Reduced etomidate dose may be required. | Major |
| Propofol, Thiopentone | Additive CNS and cardiovascular depressant effects. | Moderate |
| Succinylcholine | Etomidate may prolong the duration of neuromuscular blockade. | Moderate |
| CYP3A4 Inducers (e.g., Rifampicin, Carbamazepine) | May increase metabolism of etomidate, potentially reducing its effect. | Moderate |
| CYP3A4 Inhibitors (e.g., Ketoconazole, Erythromycin) | May decrease metabolism of etomidate, potentially prolonging its effect. | Moderate |
7. Patient Counselling
- Do inform your anesthesiologist about all allergies, especially to medications.
- Do disclose your complete medical history, especially adrenal, liver, or seizure disorders.
- Do not consume food or liquids as directed before surgery (typically 6-8 hours fasting).
- Do not drive, operate machinery, or make important decisions for at least 24 hours after the procedure.
8. Toxicology & Storage
Overdose: Profound and prolonged CNS depression (coma), cardiovascular depression (hypotension, bradycardia), apnea, and loss of protective reflexes.
Storage: Store below 25°C. Protect from light. Do not freeze. The solution is clear and colorless. Do not use if discolored or if particulate matter is present. For single use only; discard any unused portion.