Sedatives, Barbiturates, and Anxiolytics

Neurodepressants: Sedatives, Barbiturates, and Anxiolytics

Neurodepressants are drugs that decrease the activity of the central nervous system (CNS). They are used for their hypnotic, sedative, anticonvulsant, and anxiolytic effects.

1. Sedatives

  • Cause relaxation and drowsiness.
  • Examples include benzodiazepines, barbiturates, and certain antihistamines like hydroxyzine.
  • Used for:
    • Insomnia
    • Pre-anesthesia (midazolam)
    • Management of alcohol withdrawal syndrome

2. Anxiolytics

  • Most commonly used are benzodiazepines like alprazolam, lorazepam, and diazepam.
  • Used for:
    • Anxiety disorders, panic attacks
    • Short-term insomnia
    • Muscle relaxation
    • Epilepsy (diazepam, clonazepam)
  • Risks: tolerance, excessive sedative effects, anterograde amnesia, and dependence.

3. Barbiturates

  • Examples include phenobarbital, thiopental, and amobarbital.
  • Used as:
    • Anticonvulsants (phenobarbital for epilepsy)
    • Anesthetic induction (thiopental for general anesthesia)
    • Control of elevated intracranial pressure
  • Disadvantages: Causes respiratory depression, tolerance, dependence, and is lethal in overdose, which led to their replacement by benzodiazepines.

Comparison Table: Barbiturates vs. Benzodiazepines

FeatureBarbituratesBenzodiazepinesOther
ReceptorGABAaGABA_aGABAaGABA_aGABA, H1, serotonin
Safety in OverdoseLowHigher than barbituratesVariable
DependenceHighModerate/HighVariable
IndicationsEpilepsiesAnxiety, insomniaBupirone

Clinical Considerations

  • Use should be short-term.
  • Contraindicated in pregnancy, myasthenia gravis, sleep apnea, and when consuming alcohol or opioids because it can potentiate their effects, leading to coma or respiratory depression.

Mechanism of Action

1. Barbiturates
  • Acts on the GABAaGABA_a receptor, prolonging the duration of the opening of chloride channels.
  • This decreases neuronal excitability, producing sedation, anesthesia, and anticonvulsant effects.
2. Benzodiazepines
  • Acts on the alpha subunit of the GABAaGABA_a receptor, increasing the frequency of the opening of chloride channels.
  • This causes an anxiolytic, sedative, muscle relaxant, anticonvulsant, and hypnotic effect.
3. Others (Buspirone, Antihistamines)
  • These drugs have different mechanisms of action compared to barbiturates and benzodiazepines.