phenobarbital

Phenobarbital is a long-acting barbiturate used primarily as an anticonvulsant and as a sedative. It acts as a positive allosteric modulator of the GABA-A receptor, increasing chloride ion conductance and enhancing neuronal inhibition.

Medical uses include long-term control of various seizure types in both adults and children, such as partial and generalized tonic-clonic seizures. It is also employed for neonatal seizures and, in some settings, as a sedative adjunct in preoperative care or as part of treatment for alcohol withdrawal. Because of its strong CNS depressant effects, it is not typically a first-line anticonvulsant today, but remains in use where other options are unsuitable or ineffective.

Pharmacokinetics and pharmacology: phenobarbital has a long half-life, often in the range of about 53 to 118 hours in adults, allowing once- or twice-daily dosing. It can be given orally or by injection for acute situations. The drug is largely metabolized in the liver and is a potent inducer of hepatic enzymes, which can reduce the effectiveness of other medications and alter the metabolism of itself over time. It is excreted mainly as metabolites in the urine. Caution is advised in liver disease, porphyria, and pregnancy.

Adverse effects and safety: common effects include drowsiness, cognitive slowing, dizziness, and at higher doses respiratory depression or hypotension. There is a risk of dependence and withdrawal on discontinuation. Phenobarbital can interact with many drugs and with alcohol, often enhancing sedation and altering drug levels. It can reduce the effectiveness of oral contraceptives and anticoagulants.

Overdose and management: treatment is supportive and may involve activated charcoal if ingestion is recent; there is no specific antidote. Monitoring of airway, breathing, and circulation is essential.

Legal status: phenobarbital is a Schedule IV controlled substance in many countries.

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