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  • Etomidate

     

    Etomidate (Amidate™) is short-acting intravenous anesthetic agent first developed in 1964. It is available and used in the United Kingdom, Europe, New Zealand, United States, but not Australia.

    Advocates highlight etomidate's hemodynamic stability when used for induction. Critics point to the well-established adrenocortical suppression, and wide-range of suitable alternatives (propofol, ketamine, thiopentone) in trained hands.

    A. Physiochemistry

    • Carboxylated imidazole
    • 2 isomers - only R(+) hypnotic
    • Haemodynamic stability, minimal respiratory depression, cerebral protection, wide margin of safety.
    • Originally formulated in propylene glycol (painful), now in soybean lipid.

    B. Pharmacokinetics

    1. Dose - 0.3 mg/kg (0.1-0.4 mg/kg)
    2. Absorption - IV
    3. Distribution - 4 L/kg
    4. Protein binding - 75% (like thiopentone)
    5. Onset 30-60s ; Offset
    6. Metabolism - alpha1 ½ 2.5m, alpha2 ½ 30m, tß½ 3.5h; hepatic ester hydrolysis of ester side chain.
    7. Clearance - 20 mL/kg/min

    C. Pharmacodynamics

    1. Mech - probably by GABAa receptors.
    2. CNS - hypnosis; no analgesic action; ⇣ CBF and CMRO2
    3. CVS - stable; may have slight dec MAP 15% due to ⇣ SVR.
    4. Resp - minimal; sometimes brief hypoventilation or apnoea post-induction.
    5. Endo - adrenocortical suppression - inhibits 11ß-hydroxylase (11-deoxycortisol → cortisol). Temporary & reversed by vit C.
      • ⇡ ICU mortality when used for sedation.
    6. SEs - excitatory phenom, involuntary muscle movement (50%), PONV (30%), thrombophlebitis (20%), pain on injection.
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