16.6: Sedatives and Hypnotics Drugs: Barbiturates

Sedatives and hypnotics encompass a drug class that acts on the central nervous system (CNS) to alleviate anxiety, promote relaxation and induce sleep.These drugs function by amplifying the actions of the neurotransmitter γ-aminobutyric acid (GABA), resulting in reduced neuronal activity. Barbiturates, a subset of sedatives and hypnotics first synthesized in the late 1800s, are categorized into ultra-short, short, intermediate, and long-acting groups based on their duration of effect. A key representative of this class, phenobarbital, exhibits a unique structure consisting of a pyrimidine ring at its core, with additional phenyl and ethyl groups attached. Barbiturates enhance GABA's action at the GABA_A receptor, leading to neuronal hyperpolarization and reduced excitability. They also can inhibit the activity of excitatory neurotransmitters such as glutamate. Therapeutically, barbiturates demonstrate sedative, hypnotic, anticonvulsant, anesthetic effects, and muscle-relaxing properties. In a clinical setting, they treat conditions such as epilepsy, induce comas in traumatic brain injury patients, and as a secondary treatment for insomnia, although they are rarely used for insomnia due to their safety profile. Benzodiazepines and z-drugs are the preferred treatment for insomnia.

Barbiturates are not without their adverse effects. These include drowsiness, confusion, respiratory depression, and the potential for physical dependence with prolonged use. Furthermore, barbiturates can interact with other CNS depressants, like alcohol, increasing their effects and potentially leading to heightened sedation or respiratory depression. Barbiturates are potent inducers of CYP450 enzymes; this accelerates the metabolism of other drugs and reduces their efficacy. In cases of overdose, barbiturates can cause severe CNS depression, which may lead to coma or death. Treatment of overdose typically involves supportive care and specific antidotes, such as sodium bicarbonate, to accelerate urinary excretion.

Despite these potential risks, barbiturates remain essential in specific clinical scenarios due to their potent CNS effects. Although barbiturates remain vital in specific cases, their use has sharply declined due to the high risk of dependence and respiratory depression. Safer alternatives, like benzodiazepines and non-benzodiazepine sedative-hypnotics, now offer a better safety profile.

Sedatives and hypnotics are drugs that reduce anxiety, induce calmness, or promote sleep by suppressing the CNS.

Barbiturates, a class of sedative-hypnotics derived from barbituric acid, are classified based on their duration of action.

GABA's effects at the GABA_A receptor, causing neuronal hyperpolarization and reduced excitability.

Therapeutically, they exhibit sedative, hypnotic, anticonvulsant, anesthesia-inducing, and muscle-relaxing effects.

Clinically, barbiturates like phenobarbital help manage epilepsy, induce coma in brain injury and serve as a second-line insomnia treatment.

Their adverse effects include drowsiness, confusion, respiratory depression, and physical dependence. They can interact with other CNS depressants, intensifying their effects.

Overdose can cause severe CNS depression, leading to coma or even death.

Treatment of barbiturate poisoning includes supportive care and specific antidotes like sodium bicarbonate to enhance urinary excretion.

Though clinically invaluable, barbiturates are being replaced by safer alternatives like benzodiazepines.