Barbiturates Flashcards
What is the mechanism of action of barbiturates?
Enhance GABA effects, but bind at a different site than benzodiazepines.
Glutamate receptor inhibition.
Blocks sodium channels at high doses, exerting an anesthetic effect.
Compare barbiturates to benzodiazepines.
Barbiturates are stronger and more effective, but less safe.
Why have benzodiazepines replaced barbiturates?
Barbiturates:
- Induce rapid tolerance.
- Induce drug-metabolizing enzymes.
- Cause physical dependence.
- More withdrawal symptoms.
- Produce coma at toxic doses.
How are barbiturates classified?
- Long-acting.
- Short-acting.
- Ultra-short-acting.
What is the duration of action of long-acting barbiturates?
1-2 days.
What is the duration of action of short-acting barbiturates?
3-8 hours.
What is the duration of action of ultra-short-acting barbiturates?
20 minutes.
List a long-acting barbiturate.
Phenobarbital.
List short-acting barbiturates.
Pentobarbital.
Secobarbital.
Amobarbital.
List a ultra-short-acting barbiturate.
Thiopental.
What are long-acting barbiturates useful for?
Treatment of tonic-clonic seizures, status epilepticus, eclampsia, and febrile seizures.
What are short-acting barbiturates useful for?
Sedative and hypnotic, but NOT antianxiety.
What are ultra-short-acting barbiturates useful for?
Used IV to induce anesthesia.
What effect do barbiturates exert at low doses?
Sedation.
What effect do barbiturates exert at higher doses?
Hypnosis then anesthesia.
What effect do barbiturates exert at toxic doses?
Respiratory depression, coma, and death.
What occurs with chronic barbiturate use?
Tolerance and stronger dependence compared to benzodiazepines.
What do barbiturates lack?
Like benzodiazepines, they lack analgesic action.
How do barbiturates depress respiration?
By suppressing the hypoxic and chemoreceptor response to CO2.
What effect do barbiturates exert on enzyme induction?
Induction of CYP450, increasing the metabolism of other drugs metabolized by CYP450, decreasing their effect.
What are the therapeutic uses of barbiturates?
- Anesthesia.
- Anticonvulsant.
- Anxiolytic.
- Hypnotic.
Which barbiturate is the drug of choice for treating young children with recurrent febrile seizures?
Phenobarbital.
Why should phenobarbital be used cautiously with adults and children?
Suppresses cognitive development in children, and cognitive performance in adults.
What are the hypnotic effects of barbiturates?
Suppresses REM sleep more than other stages,
Decreases sleep latency, the number of awakenings, and the duration of REM sleep.
How are barbiturates absorbed?
Orally, and distributed widely throughout the body.
Why does thiopental have a short duration of action?
Like all barbiturates, it is redistributed from the brain to other tissues, which decreases the duration of action.
Why are barbiturates never used for pregnancy?
They cross the placenta and depress the fetus’ respiration.
How are barbiturates metabolized and excreted?
Metabolized in the liver, excreted in the urine.
What are the adverse effects of barbiturates?
CNS:
- Drowsiness.
- Impaired concentration.
- Mental and physical sluggishness.
Drug hangover: hypnotic doses cause a feeling of tiredness after the patient awakes.
Why should antiepileptic women taking oral contraceptives avoid taking barbiturates?
Phenobarbital increases the activity of hepatic drug-metabolizing enzymes such as CYP450, decreasing the duration of action of drugs.
Why are barbiturates contraindicated for patients with acute intermittent porphyria?
Barbiturates increase porphyria synthesis.
How do barbiturates increase porphyria synthesis?
By inducing ALA synthetase.
What effect does increased porphyria synthesis have?
CNS dysfunction, coma, and death.
What happens when barbiturates are abruptly stopped?
Tremors.
Anxiety.
Weakness.
Restlessness.
Nausea.
Vomiting.
Seizures.
Delirium.
Cardiac arrest.
What are the signs of barbiturate poisoning?
- Respiratory depression.
- Central cardiovascular depression.
- Shock-like condition with shallow, infrequent breathing.
How is barbiturate poisoning treated?
- Hemodialysis.
- Artificial respiration and purging the stomach.
- Alkalization of the urine by sodium bicarbonate.
