Hypnotics and Anxiolytics: Part 5.

Second to benzodiazepines, lies a group of anxiolytics and hypnotics called barbiturates. Barbiturates are less likely to be used today, due to their rapid tolerance, physical dependence and withdrawal symptoms.

MOA: Barbiturates interact with GABA receptors to prolong the duration of opening of chloride ion channels, usually accompanied by hypnotics and sedative effects. In addition, barbiturates also block the excitatory glutamate receptors to decrease neural activity.

ADR:

• CNS disturbances.
• Drug hangover.
• CYP450 enzyme induction.
• Addiction.
• Potential toxicity in high doses. (treatable using aminophylline)
• Sudden withdrawal symptoms.

Examples of CNS disturbances.

• Drowsiness.
• Vertigo.
• Impaired concentration.
• Mental and physical sluggishness.

Toxicity symptoms, usually observed in high doses.

• Respiratory and cardiac arrest.
• Severe drowsiness.
• Slurry speech.
• Staggering.
• Severe confusion and weakness.
• Slowed heart beats.

Sudden withdrawal symptoms.

• Tremors.
• Anxiety.
• Weakness.
• Restlessness.
• Nausea and vomiting.
• Delirium.
• Cardiac arrest.

TU:

• As anesthetics.
• As anti-convulsants.
• Anxiety.
• Insomnia.
• Nervous tension.

PRCTN:

• Pregnant and lactating mothers.
• Kidney and liver disease.
• Diabetic patients.
• Patients with prophyrias.

EX:

Long-acting Barbiturates (1-2 days).

• Phenobarbital.

Short-acting Barbiturates (3-8 hrs).

• Amobarbital.
• Pentobarbital (also blocks the high frequency sodium channels).
• Secobarbital.

Ultra-short acting Barbiturates (20 min).

• Thiopental.