Etomidate

Drug Class: Hypnotic/anesthetic agent | Pharmacological Group: Non-barbiturate intravenous anesthetic

Mechanism of Action: Etomidate is a short-acting intravenous anesthetic agent that produces hypnosis by enhancing gamma-aminobutyric acid (GABA)-mediated inhibitory neurotransmission in the central nervous system. It binds to the beta subunit of the GABA-A receptor, increasing the frequency of chloride channel opening, leading to hyperpolarization of neurons and inhibition of neuronal firing. This results in rapid induction of anesthesia with minimal cardiovascular and respiratory depression.

Pharmacodynamics: Etomidate produces dose-dependent hypnotic effects, with loss of consciousness occurring within one circulation time. It has minimal effects on cardiovascular function, maintaining arterial blood pressure and cardiac output, making it suitable for patients with cardiovascular compromise. It also causes a transient decrease in cerebral blood flow and intracranial pressure, but may increase cerebral metabolic rate. Etomidate suppresses adrenocortical steroid synthesis by inhibiting 11-beta-hydroxylase, leading to decreased cortisol production, which can be clinically significant with prolonged infusion or repeated dosing.

Common:

• Pain on injection
• Myoclonus
• Involuntary muscle movements
• Apnea (transient)
• Nausea and vomiting (especially in dogs and cats)
• Excitement during induction (if not adequately premedicated)

Serious / Severe:

• Adrenocortical suppression (with prolonged use)
• Cardiovascular collapse (rare, usually with overdose or in compromised patients)
• Respiratory depression or arrest
• Anaphylaxis (rare)

Rare:

• Thrombophlebitis
• Hemolysis (with propylene glycol formulation)
• Hyperkalemia (in some species)
• Seizures (in patients with seizure disorders)

Signs of Toxicity:

• Prolonged anesthesia
• Severe respiratory depression or apnea
• Hypotension
• Cardiovascular collapse
• Myoclonus and seizures (in severe cases)

Emergency Treatment Protocol: Treatment is primarily supportive. Maintain airway and provide ventilatory support (oxygen, mechanical ventilation). Administer intravenous fluids to support blood pressure. Use vasopressors (e.g., dopamine, norepinephrine) if hypotension persists. Monitor cardiac function and treat arrhythmias if they occur. Since etomidate suppresses adrenocortical function, consider corticosteroid supplementation (e.g., hydrocortisone) in cases of prolonged overdose or if adrenal insufficiency is suspected. There is no specific antidote; recovery is dependent on metabolism and elimination.

Etomidate is not approved for use in food animals in many countries. If used extra-label, withdrawal times must be determined based on regulatory guidelines (e.g., FARAD in the US). Generally, a withdrawal period of at least 24-48 hours is recommended, but consult regulatory authorities.

Storage Temperature: Store at controlled room temperature (20-25°C, excursions permitted to 15-30°C).

Handling & Special Conditions: Protect from freezing. Use only if solution is clear and free of particulate matter. Discard unused portions after opening.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Not FDA-approved for veterinary use; approved for human use in the US.

Extra-Label (Off-Label) Use: In the US, etomidate is not FDA-approved for veterinary use; its use in animals is extra-label. Under AMDUCA, extra-label use is permitted by or on the order of a licensed veterinarian within a valid veterinarian-client-patient relationship, provided that withdrawal times are extended and residues are not present in food. For food animals, a prolonged withdrawal time must be established, and use is prohibited in animals whose milk or eggs are intended for human consumption unless specific tolerance exists.