Phenobarbital is indicated for the following conditions:

• Sedative
• Hypnotic for short-term treatment of insomnia
• Pre-anesthetic medication
• Long-term anticonvulsant therapy for generalized tonic-clonic seizures and cortical focal seizures
• Emergency control of acute convulsive episodes such as status epilepticus, eclampsia, meningitis, tetanus, and toxic reactions to strychnine or local anesthetics

Phenobarbital is a barbiturate and a non-selective central nervous system (CNS) depressant. It is mainly used as a sedative-hypnotic and, at sub-hypnotic doses, as an anticonvulsant.

Phenobarbital is the longest-acting barbiturate used for its anticonvulsant and sedative-hypnotic effects in the treatment of most seizure disorders, except absence (petit mal) seizures. It acts by enhancing the effect of gamma-aminobutyric acid (GABA) at GABA receptors, increasing synaptic inhibition. This raises the seizure threshold and reduces the spread of seizure activity from the seizure focus. Phenobarbital may also inhibit calcium channels, which decreases the release of excitatory neurotransmitters. Its sedative-hypnotic action is mainly due to depression of the polysynaptic midbrain reticular formation, which regulates CNS arousal and alertness.

Suggested doses of Phenobarbital for specific indications are as follows:

Pediatric Oral Dosage:

• Preoperative: 1 mg to 3 mg/kg.
• Anticonvulsant: 1 mg to 6 mg/kg per day.

Adult Oral Dosage:

• Daytime sedative: 30 mg to 120 mg daily in 2 to 3 divided doses.
• Bedtime hypnotic: 100 mg to 320 mg.
• Anticonvulsant: 50 mg to 100 mg 2 to 3 times daily.

Pediatric Injection Dosage:

• 15 to 20 mg/kg IV over 10 to 15 min.
• Preoperative Sedation: 1 to 3 mg/kg IM/IV;
• Anticonvulsant: 4 to 6 mg/kg IM/IV per day, for 10 days. Alternatively, use 10 to 15 mg/kg IM/IV per day to reach therapeutic level more quickly. Maximum IV rate 60 mg/min.

Adult Injection Dosage:

• Insomnia: 100 to 320 mg IM/IV;
• Convulsions: 100 to 320 mg IV. Repeat if needed (maximum, 600 mg per day);
• Status Epilepticus: 10 to 20 mg/kg IV. Repeat if needed.

Concomitant use of alcohol or other central nervous system (CNS) depressants may produce additive CNS depressant effects, increasing sedation and respiratory depression.

Phenobarbital is contraindicated in patients with known hypersensitivity to phenobarbital or a history of latent porphyria.

The most common adverse effect is somnolence. Other less frequent effects include agitation, confusion, hyperkinesia, ataxia, CNS depression, nightmares, nervousness, psychiatric disturbances, hallucinations, insomnia, anxiety, dizziness, abnormal thinking, apnea, bradycardia, hypotension, nausea, vomiting, and constipation.

Pregnancy Category D. Phenobarbital may cause fetal harm when used during pregnancy. If used during pregnancy or if pregnancy occurs during treatment, the patient should be informed about the potential risk to the fetus. Small amounts of phenobarbital are excreted in breast milk; therefore, caution is required in nursing mothers.

Tolerance, psychological dependence, and physical dependence may develop with prolonged use. It should be used cautiously in patients with depression, suicidal tendencies, or a history of substance abuse. In patients with hepatic impairment, reduced doses and careful monitoring are required.

The toxic dose of barbiturates varies, but approximately 1 gram may cause serious poisoning in adults. Death may occur with 2–10 grams. Acute overdose causes CNS and respiratory depression. Treatment is mainly supportive and requires immediate hospitalization.

Adjunct anti-epileptic drugs, Barbiturates

Store below 30°C, away from light and moisture. Keep out of reach of children.