Barbiturates
Barbiturates
The major pharmacologic action of barbiturates is to reduce overall CNS alertness. Barbiturates used primarily as sedatives and hypnotics include:
- amobarbital
- butabarbital
- mephobarbital
- pentobarbital
- phenobarbital
- secobarbital.
On the dose
Low doses of barbiturates depress the sensory and motor cortex in the brain, causing drowsiness. High doses may cause respiratory depression and death because of their ability to depress all levels of the CNS.
Pharmacokinetics
Barbiturates are well absorbed from the GI tract, distributed rapidly, metabolized by the liver, and excreted in urine.
Pharmacodynamics
As sedative-hypnotics, barbiturates depress the sensory cortex of the brain, decrease motor activity, alter cerebral function, and produce drowsiness, sedation, and hypnosis.
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These drugs appear to act throughout the CNS; however, the RAS of the brain, which is responsible for wakefulness, is a particularly sensitive site.
Pharmacotherapeutics
Barbiturates have many clinical indications, including:
- daytime sedation (for short periods only, typically less than 2 weeks)
- hypnotic effects for patients with insomnia
- preoperative sedation and anesthesia
- relief of anxiety
- anticonvulsant effects.
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Popularity plunge
Patients develop tolerance to barbiturates more quickly than to benzodiazepines, and physical dependence on barbiturates
may occur even with a small daily dosage. In comparison, benzodiazepines are relatively effective and safe and, for these reasons, have replaced barbiturates as the sedatives and hypnotics of choice.
may occur even with a small daily dosage. In comparison, benzodiazepines are relatively effective and safe and, for these reasons, have replaced barbiturates as the sedatives and hypnotics of choice.
Drug interactions
Barbiturates may interact with many other drugs:
- They may reduce the effects of beta-adrenergic blockers (metoprolol, propranolol), chloramphenicol, corticosteroids, doxycycline, oral anticoagulants, hormonal contraceptives, quinidine, tricyclic antidepressants (TCAs), metronidazole, theophylline, and cyclosporine.
- Hydantoins, such as phenytoin, reduce the metabolism of phenobarbital, resulting in increased toxic effects.
- Their use with methoxyflurane may stimulate production of metabolites that are toxic to the kidneys.
- Their use with other CNS depressants (especially alcohol) may cause excessive CNS depression.
- Valproic acid may increase barbiturate levels.
- Monoamine oxidase inhibitors (MAOIs) inhibit the metabolism of barbiturates, increasing their sedative effects.
- When barbiturates are taken with acetaminophen, the risk of liver toxicity increases.
Warning!Adverse reactions to barbiturates
Barbiturates may have widespread adverse effects.
S.O.S. for CNS
Central nervous system (CNS) reactions include:
- drowsiness
- lethargy
- headache
- depression.
Heart of the matter
Cardiovascular and respiratory effects include:
- mild bradycardia
- hypotension
- hypoventilation
- spasm of the larynx (voice box) and bronchi
- reduced rate of breathing
- severe respiratory depression.
All the rest
Other reactions include:
- vertigo
- nausea and vomiting
- diarrhea
- epigastric pain
- allergic reactions.
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