Pharmacology  ·  Sedative-Hypnotic Drugs

Barbiturates and Intravenous Sedative-Hypnotics

Mechanism, hemodynamic profile, and clinical niche of each agent

Abbreviations: AMPA = alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid  ·  NMDA = N-methyl-D-aspartate  ·  ICU = intensive care unit  ·  BP = blood pressure  ·  CYP = cytochrome P450  ·  INR = international normalized ratio

Barbiturates vs. Benzodiazepines: Mechanism Comparison
FeatureBenzodiazepinesBarbituratesClinical Consequence
Binding siteAlpha-gamma subunit interfaceWithin chloride channel poreDifferent allosteric sites, additive effects
Effect on channelIncrease frequency of openingIncrease duration of openingBoth enhance chloride influx
GABA requirementRequired at all dosesRequired at therapeutic doses; direct activation at high dosesBarbiturates lack ceiling effect
Overdose riskWide safety margin in isolationRespiratory depression and death possibleExplains historic shift to benzodiazepines
Additional targetNone significantAMPA glutamate receptor inhibitionDual mechanism useful in refractory status epilepticus
Phenobarbital: Current Clinical Uses
Indication
Neonatal Seizures
  • First-line agent at most institutions
  • Loading dose 20 mg/kg intravenously
  • AMPA antagonism contributes to efficacy in neonatal physiology
Indication
Refractory Status Epilepticus
  • Third-line agent after benzodiazepines and second-line agents fail
  • Effective when GABA-A receptor downregulation limits benzodiazepine efficacy
  • Intubation readiness required at loading doses
Drug Interactions
Cytochrome P450 Induction
  • Induces CYP1A2, CYP2C9, CYP2C19, CYP3A4, and P-glycoprotein
  • Reduces warfarin efficacy — monitor INR
  • Reduces oral contraceptive efficacy — alternative contraception required
  • Reduces antiretroviral and many anticonvulsant levels
Intravenous Sedatives: Mechanism and Clinical Profile
AgentMechanismHemodynamicsBest UseKey Caution
PropofolGABA-A positive allosteric modulatorHypotension (decreased vascular resistance)Anesthesia induction, procedural sedation, ICU sedationPropofol infusion syndrome at high doses (>5 mg/kg/hr for >48 hours)
DexmedetomidineAlpha-2 adrenergic agonist (locus coeruleus)Bradycardia, hypotensionICU sedation requiring arousability; neurological assessmentTransient hypertension with rapid loading
KetamineNMDA receptor antagonistIncreases heart rate, BP, and cardiac outputHemodynamic instability, reactive airway disease, procedural analgesiaEmergence reactions (mitigate with midazolam)
EtomidateGABA-A positive allosteric modulatorMinimal — most stable induction agentSingle-dose induction in unstable patientsAdrenocortical suppression (inhibits 11-beta-hydroxylase). Do not use as infusion.
Buspirone: Key Distinctions

Buspirone is a serotonin 5-HT1A partial agonist approved for generalized anxiety disorder. It is not sedating, has no GABA-A receptor activity, produces no dependence, and has no cross-tolerance with benzodiazepines or alcohol. Onset of anxiolytic effect is delayed 1–4 weeks. It will not treat or prevent alcohol or benzodiazepine withdrawal. Patients switching from benzodiazepines must be tapered off separately.

Suggested References

Author / Organization Title Source
Katzung BG (ed) Basic and Clinical Pharmacology, 15th ed. Chapter 22: Sedative-Hypnotic Drugs McGraw-Hill, 2021
Brunton LL, Knollmann BC (eds) Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed. Chapter 17: Hypnotics and Sedatives McGraw-Hill, 2023
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