Barbiturates

Barbiturates are a class of drugs primarily used for their sedative and hypnotic properties, which act by decreasing activity in the brain. Historically important in medical treatment, these drugs have the potential to be habit-forming and can lead to fatal consequences if combined with substances such as alcohol.

Barbituric acid, the parent structure of all barbiturates

Overview

Barbiturates consist of structurally related compounds known for their sedative, hypnotic, and in some cases, anticonvulsant activities. Notably, phenobarbital and mephobarital are recognized for their anticonvulsant properties.

Mechanism of Action

As central nervous system (CNS) depressants, barbiturates exhibit nonselective sedative and hypnotic activities. They function by enhancing the effect of neurotransmitter gamma aminobutyric acid (GABA), which leads to suppressed seizure activity in the case of anticonvulsant barbiturates like phenobarbital.

Usage

Introduced in the United States during the 1950s, barbiturates such as amobarbital, butabarbital, pentobarbital, and secobarbital were primarily used as sedatives, hypnotics, and preanesthetic agents. Their use has waned due to the development of more effective and better-tolerated alternatives like benzodiazepines. Current uses for barbiturates encompass short-term insomnia treatment and as a preanesthetic agent.

Liver Safety

There's a marked association between phenobarbital and instances of idiosyncratic acute liver injury, bearing similarity to the hepatotoxicity caused by other anticonvulsants such as phenytoin and carbamazepine. Contrarily, conventional sedative barbiturates are not commonly linked to liver enzyme elevations, making clinically evident acute liver injury from these drugs exceedingly rare.

Dosage and Administration

The typical dosage for secobarbital in adults is 100 mg before bedtime or 200 to 300 mg approximately 1 to 2 hours before a surgical procedure. Notably, barbiturates like butalbital, mephobarbital, methohexital, and pentobarbital are no longer available in the U.S. Due to its potential for dependency and abuse, secobarbital is classified as a Schedule II substance. Common side effects encompass drowsiness, sedation, nausea, hypotension, headaches, and rashes.

FDA Approval and Anesthetics

Historically, halothane became a popular choice for general anesthesia after its introduction in 1956. However, reports of liver injury possibly attributed to halothane began emerging. Despite initial resistance, the hepatotoxicity of halothane was eventually acknowledged. The hepatotoxic mechanism, tied to its metabolism by the liver enzyme system (specifically CYP 2E1), led to its reduced use. Newer halogenated anesthetics such as enflurane, isoflurane, desflurane, and sevoflurane have since been introduced, with rare instances of acute liver injury reported for all.

See Also

• Desflurane
• Enflurane
• Halothane
• Isoflurane
• Sevoflurane

• Dailymed label info on Barbiturates
• FDA Barbiturates

Barbiturates Resources
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