Anaes · Intravenous induction agents

Thiopental

Also known as Sodium thiopentone · Thiopentone · Thiobarbiturate · Barbiturate induction agent · Pentothal

Thiopental (sodium thiopentone) is the classic barbiturate induction agent — the first true intravenous induction drug, introduced in 1934, and still the agent of choice for rapid-sequence induction in obstetric general anaesthesia, for status epilepticus, and for barbiturate-coma neuroprotection. The framework rests on four exam-critical ideas: it is a thiobarbiturate whose sulfur atom at position 2 confers ultra-high lipophilicity, and it acts at the GABA-A receptor by INCREASING the DURATION of chloride channel opening (distinct from the benzodiazepines, which increase the FREQUENCY), with direct channel opening at high doses; its signature speed — onset in 10 to 30 seconds and recovery in 5 to 10 minutes — is the property of instant blood-brain-barrier penetration followed by rapid redistribution from the vessel-rich to the muscle compartment, while its hepatic metabolism has a low extraction ratio so the context-sensitive half-time rises steeply and the drug accumulates with repeated boluses or infusion, making it unsuitable for maintenance; it causes a 10 to 25 percent drop in blood pressure from myocardial depression and venodilation with reflex tachycardia (less hypotension than propofol but more tachycardia) yet is remarkably safe in pregnancy, sparing the uteroplacental circulation; and acute intermittent porphyria is the absolute contraindication because barbiturates induce ALA synthase and precipitate a porphyric crisis, while intra-arterial injection is catastrophic from crystallisation in arterioles. Built on the caesarean-section general-anaesthesia practice review (Helmer 2026), the obstetric GA pharmacology best-practice paper (Craig 2026), the vagus-nerve-stimulation refractory status epilepticus study (Parak 2026), the neuro-sedation for intracranial hypertension work (Ravaux 2026), the anaesthetic allergy review (Lisiecka 2026), the barbiturate reference (Lewis 2026), the GABA-A receptor gallic-acid/diazepam work (Yana 2026), and the ketamine-versus-etomidate RSI comparison (Chilingarashvili 2026).