Pharm 101: Thiopentone

Class

Barbiturate

Pharmacodynamics
  • Facilitate actions of GABA in CNS
  • Bind to specific GABA-A receptor subunits at CNS neuronal synapses
  • In contrast to benzodiazepines, increase duration of GABA-gated chloride channel openings
  • At high concentrations, may be GABA-mimetic, directly activating chloride channels
Organ system effects
  • CNS:
    • Dose-dependent depression ranging from sedation to general anaesthesia
    • Decreased CMR, blood flow and ICP
    • Decreased cerebral oxygen consumption
    • No analgesic effect, possible hyperalgesia
  • CVS:
    • Hypotension due to vasodilatation (less than that of propofol)
    • Negative inotrope
    • Compensatory tachycardia
  • Respiratory depression
Pharmacokinetics
  • Highly lipid soluble
  • 83% protein bound
  • Distribution to highly vascular tissue and rapidly crosses BBB, then rapid redistribution to body fat
  • Distribution half-life 2-4 mins
  • Elimination half-life 11 hours
  • Hepatic metabolism
  • < 1% excreted unchanged in urine
Clinical uses
  • Rapid Sequence Induction (RSI):
    • Induction dose 3-5 mg/kg
    • Onset within 30 seconds
    • Duration of action 5-10 mins
Adverse effects
  • Extension of organ system effects including hypotension, respiratory depression
  • Pain on injection
  • Hyperalgesia
  • Rarely, porphyric crisis due to induction of ALA synthase in liver
  • Severe tissue injury +/- gangrene in accidental intra-arterial injection
Precautions/contraindications
  • Acute porphyria
  • Hypovolaemia
  • Cardiovascular disease
  • Rapid administration of neuromuscular blocking drugs may result in precipitation of insoluble thiopentone acid
Further reading
References
  • Katzung BG. Basic & Clinical Pharmacology. 14th ed. United States of America: McGraw-Hill Education; 2018. 383-389, 450-454 p.
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MBBS (UWA) CCPU (RCE, Biliary, DVT, E-FAST, AAA) Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Editor-in-chief of the LITFL ECG Library. Twitter: @rob_buttner

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