Barbiturates: Mechanism of Action and Classification
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Questions and Answers

What is the primary use of barbiturates as a mild sedative?

  • To treat tonic-clonic seizures
  • To treat depression
  • To induce anesthesia
  • To relieve anxiety and nervous tension (correct)

    • What is the effect of phenobarbital on cognitive performance in children?

  • It has no effect on cognitive performance
  • It increases seizures
  • It improves cognitive performance
  • It depresses cognitive performance (correct)

    • What is the adverse effect of barbiturates on patients with acute intermittent porphyria?

  • It has no effect on porphyrin synthesis
  • It increases the risk of seizures
  • It increases porphyrin synthesis (correct)
  • It decreases the risk of respiratory depression

    • What is the effect of benzodiazepines on sleep patterns?

    <p>They have no effect on sleep patterns</p> Signup and view all the answers

    What is the mechanism of action of benzodiazepines?

    <p>They act on the GABA receptors</p> Signup and view all the answers

    What is the characteristic of benzodiazepines that makes them safer than barbiturates?

    <p>They have a wide safety margin</p> Signup and view all the answers

    What is the effect of abrupt withdrawal from barbiturates?

    <p>It causes tremors and anxiety</p> Signup and view all the answers

    What is the contraindication of barbiturates in pregnancy?

    <p>They depress the fetus</p> Signup and view all the answers

    What is a desirable characteristic of benzodiazepines when used as hypnotics?

    <p>Short elimination half-life</p> Signup and view all the answers

    Where are benzodiazepines primarily metabolized?

    <p>Liver</p> Signup and view all the answers

    What is the primary mechanism of benzodiazepines' anxiolytic effect?

    <p>Enhancing GABAergic transmission in neurons with α2 subunit</p> Signup and view all the answers

    What is the receptor subtype involved in the hypnotic effects of benzodiazepines?

    <p>α1-GABAA</p> Signup and view all the answers

    What is the primary effect of benzodiazepines on memory?

    <p>Temporary impairment of memory</p> Signup and view all the answers

    What is the mechanism of benzodiazepines' muscle relaxant effect?

    <p>Increase of presynaptic inhibition in the spinal cord</p> Signup and view all the answers

    Why are benzodiazepines not recommended for use during pregnancy?

    <p>They can depress the CNS of the newborn</p> Signup and view all the answers

    What is the therapeutic use of Triazolam?

    <p>Insomnia</p> Signup and view all the answers

    What is the main use of benzodiazepines as preanesthetic medication?

    <p>To induce amnesia</p> Signup and view all the answers

    What is a common adverse effect of benzodiazepines?

    <p>Drowsiness and confusion</p> Signup and view all the answers

    What is the mechanism of action of flumazenil?

    <p>Competitive antagonism</p> Signup and view all the answers

    What is the duration of action of flumazenil?

    <p>About 1 hour</p> Signup and view all the answers

    What is the main advantage of buspirone over benzodiazepines?

    <p>It has no anticonvulsant or muscle relaxant properties</p> Signup and view all the answers

    What is the mechanism of anxiolytic action of buspirone?

    <p>Acting as a 5-HT1A receptor partial agonist</p> Signup and view all the answers

    What can happen if flumazenil is administered to a patient who has been taking benzodiazepines for a long time?

    <p>The patient will experience withdrawal symptoms</p> Signup and view all the answers

    What is the main difference between benzodiazepines and atypical anxiolytics?

    <p>Atypical anxiolytics have no anticonvulsant properties</p> Signup and view all the answers

    What is the primary site of action of barbiturates?

    <p>Mesenocephalic reticular activating system (RAS)</p> Signup and view all the answers

    How do barbiturates affect GABA?

    <p>They enhance GABA effect or stimulate its release</p> Signup and view all the answers

    What is the primary mechanism of action of barbiturates?

    <p>They increase the duration of GABA-gated channel openings</p> Signup and view all the answers

    What is the effect of barbiturates on the CNS at low doses?

    <p>Sedation</p> Signup and view all the answers

    What is the effect of high doses of barbiturates on the CNS?

    <p>All of the above</p> Signup and view all the answers

    What is the effect of barbiturates on respiratory system?

    <p>Respiratory depression</p> Signup and view all the answers

    What is the effect of phenobarbitone on the liver?

    <p>Inducer of liver enzymes</p> Signup and view all the answers

    What is the primary therapeutic use of ultra-short-acting barbiturates?

    <p>Anesthesia induction</p> Signup and view all the answers

    What is the time frame for the anxiolytic effects of buspirone to manifest?

    <p>More than a week</p> Signup and view all the answers

    What is a characteristic of buspirone that makes it a preferred choice?

    <p>Minimal abuse liability</p> Signup and view all the answers

    What is the main difference between Z compounds and benzodiazepines?

    <p>They are less effective as anticonvulsants</p> Signup and view all the answers

    What is the mechanism of action of melatonin receptor agonists?

    <p>Stimulating MT1 and MT2 receptors</p> Signup and view all the answers

    What is an advantage of melatonin receptor agonists?

    <p>Minimal potential for abuse</p> Signup and view all the answers

    What is the mechanism of action of suvorexant?

    <p>Blocking the action of orexin</p> Signup and view all the answers

    What is a characteristic of buspirone in terms of its use in anxiety disorders?

    <p>Effective in generalized anxiety disorders</p> Signup and view all the answers

    What is the treatment for overdose with Z compounds?

    <p>Flumazenil</p> Signup and view all the answers

    Study Notes

    Barbiturates

    • Classified according to their durations of action
    • Site of action: depress neurons and synapses of the mesenocephalic reticular activating system (RAS), reducing electrical activity of the cortex
    • Mechanism of action:
      • GABA potentiators, enhancing GABA effect or stimulating its release
      • Activate inhibitory GABAA receptors
      • Promote GABA-induced chloride current
      • Increase duration of GABA-gated channel openings
      • May be GABA-mimetic (high concentration) by direct activation of chloride channels through binding sites distinct from benzodiazepines (BDZ) binding sites
    • Pharmacokinetics:
      • Absorption: well absorbed
      • Distribution: thiobarbitone is highly lipid soluble and crosses BBB rapidly to the brain and then redistributed in less vascular tissues
      • Excretion: phenobarbitone is excreted unchanged in the urine and its excretion is increased significantly by alkalinization of urine

    Effects of Barbiturates

    • Depression of CNS:
      • At low doses: sedation
      • At high doses: hypnosis, anesthesia, coma, and death
    • Respiratory depression:
      • Lethal dose: suppresses hypoxic and chemoreceptor response to CO2, and overdose is followed by respiratory depression and death
    • CVS:
      • High dose: hypotension due to suppression of ganglionic transmission and suppression of VMC
    • Liver:
      • Enzyme inducer and decreases effect of many drugs

    Therapeutic Uses of Barbiturates

    • Anesthesia: selection of a barbiturate is strongly influenced by the desired duration of action
    • Sedative/hypnotic: used to relieve anxiety, nervous tension, and insomnia
    • Anticonvulsant: phenobarbital is used in long-term management of tonic-clonic seizures, status epilepticus, and eclampsia

    Adverse Effects of Barbiturates

    • CNS: drowsiness and mental confusion
    • Hangover: hypnotic doses of barbiturates produce a feeling of tiredness well after the patient wakes
    • Porphyrin synthesis: increases porphyrin synthesis and is contraindicated in patients with acute intermittent porphyria
    • Abuse and dependence: tolerance develops on repeated use, and abrupt withdrawal may cause tremors, anxiety, weakness, restlessness, nausea, and vomiting, seizures, delirium, and cardiac arrest

    Benzodiazepines

    • Advantages:
      • Wide safety margin
      • Little CV and respiratory depression
      • Fewer drug interactions
      • Lower abuse liability and least to alter sleep pattern
      • Specific antagonist flumazenil
    • Mechanism of action:
      • Targets GABAA receptors
      • GABAA receptors are composed of a combination of five α, β, and γ subunits that span the postsynaptic membrane
    • Pharmacokinetics:
      • Absorption and distribution: lipophilic, rapidly and completely absorbed after oral administration, and distribute throughout the body and penetrate into the CNS
      • Duration of action: half-lives of benzodiazepines are important clinically, as the duration of action may determine the therapeutic usefulness

    Actions of Benzodiazepines

    • Reduction of anxiety:
      • At low doses, benzodiazepines are anxiolytic
      • Reduce anxiety by selectively enhancing GABAergic transmission in neurons having the α2 subunit in their GABAA receptors, thereby inhibiting neuronal circuits in the limbic system of the brain
    • Sedative/hypnotic:
      • All benzodiazepines have sedative and calming properties, and some can produce hypnosis at higher doses
    • Anticonvulsant:
      • Mediated by α1-GABAA receptors
    • Muscle relaxant:
      • At high doses, benzodiazepines relax the spasticity of skeletal muscle, probably by increasing presynaptic inhibition in the spinal cord, where the α2-GABAA receptors are largely located

    Therapeutic Uses of Benzodiazepines

    • Anxiolytic (in GAD, panic disorders)
    • Insomnia (triazolam)
    • Anticonvulsants (clonazepam, lorazepam, and diazepam)
    • Preanesthetic medication (amnesia)
    • Muscle spasm (diazepam)
    • Alcohol withdrawal syndrome

    Adverse Effects of Benzodiazepines

    • Drowsiness and confusion
    • Cognitive impairment
    • Ataxia
    • Triazolam: dose-dependent change in sleep pattern: dec REM and inc NREM and tolerance
    • Impairment of mental and motor functions
    • All of these effects can greatly impair driving and other psychomotor skills, especially if combined with ethanol
    • Rebound insomnia
    • Hypotension and respiratory depression
    • Dependence and abuse

    New Anxiolytics and Hypnotics

    • Atypical anxiolytics:
      • Buspirone
      • Ipsapirone
      • Gepirone
    • Buspirone:
      • Relieves anxiety without causing marked sedative, hypnotic, or euphoric effects
      • No anticonvulsant or muscle relaxant properties
      • Acts as a partial agonist at brain 5-HT1A receptors
      • Anxiolytic effects take more than a week
      • Unsuitable for management of acute anxiety states
      • No rebound anxiety or withdrawal signs on abrupt discontinuation
      • Minimal abuse liability
    • Other hypnotics:
      • Z compounds (zolpidem, zaleplon, and zopiclone)
      • Melatonin receptor agonists (ramelteon and tasimelteon)
      • Suvorexant (orexin receptor antagonist)

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