Lecture on Barbiturates

Introduction to Barbiturates

• Barbiturates are a class of drugs that affect the central nervous system as depressants.
• They have sedative, hypnotic, and anti-convulsant properties.

Mechanism of Action

• Target: Act on GABAergic synapses, altering modularity in the synapse.
• Receptors: Bind to GABA A type receptors.
  • Allow chloride ions to enter post-synaptic neurons.
  • Enhance the inhibitory effect of GABAergic synapses.

Binding Sites

• Barbiturate Binding Site: Interface between alpha and beta subunit of GABA receptors.
• Benzodiazepine Binding Site: Interface between alpha and gamma subunit.

Effects on Chloride Ion Channels

• Barbiturates increase chloride ion influx by prolonging channel open duration.
• Differ from benzodiazepines, which increase opening frequency but not duration.
• Result: Increased chloride influx leads to hyperpolarization, reducing action potential firing probability.

Uses of Barbiturates

• Sedatives: Historically used (e.g., Phenobarbital).
• Anesthesia: Short-acting barbiturates like Thiopental for rapid induction.
• Anti-convulsants: Used for seizure control.

Adverse Effects

• CNS Depression: Can cause drowsiness, sedation, and respiratory depression.
• Overdose Risks: Potentially fatal.
• Dependence: Risk of addiction.
• Drug Interactions: Induce hepatic enzymes (CYP450), affecting metabolism of other drugs.

Precautions

• Use under clinical guidance due to risks of interactions and changes in pharmacokinetics.

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