Generic
Phenobarbital
12 brands available in the market
At a glance
Phenobarbital is a barbiturate used as a sedative, hypnotic (short-term treatment of insomnia), pre-anesthetic, and long-term anticonvulsant. It is used for generalized tonic-clonic and cortical local seizures, and emergency control of acute convulsive episodes associated with status epilepticus, eclampsia, meningitis, tetanus, and strychnine or local anesthetic toxicity.
Description
Phenobarbital is a barbiturate, nonselective central nervous system depressant primarily used as a sedative hypnotic and as an anticonvulsant in subhypnotic doses. It acts on GABAA receptors, increasing synaptic inhibition, elevating seizure threshold, and reducing spread of seizure activity. It may also inhibit calcium channels, decreasing excitatory transmitter release.
Indications
- Sedative
- Hypnotic for short-term treatment of insomnia
- Pre-anesthetic
- Long-term anticonvulsant for generalized tonic-clonic and cortical local seizures
- Emergency control of acute convulsive episodes (status epilepticus, eclampsia, meningitis, tetanus, strychnine or local anesthetic toxicity)
Therapeutic class
Adjunct anti-epileptic drugs, Barbiturates
Pharmacological class
Barbiturate (Nonselective CNS Depressant)
Pharmacology
Phenobarbital is the longest-acting barbiturate used for its anticonvulsant and sedative-hypnotic properties. It acts on GABAA receptors, increasing synaptic inhibition, elevating seizure threshold, and reducing seizure activity spread. It may also inhibit calcium channels, decreasing excitatory transmitter release. Sedative-hypnotic effects result from effects on the midbrain reticular formation.
Mechanism of action
Increases synaptic inhibition by acting on GABAA receptors and inhibits calcium channels to elevate seizure threshold.
Dosage
Adult Dose (Oral):
- Daytime sedative: 30-120 mg daily in 2-3 divided doses
- Bedtime hypnotic: 100-320 mg
- Anticonvulsant: 50-100 mg 2-3 times daily
Pediatric Dose (Oral):
- Preoperative: 1-3 mg/kg
- Anticonvulsant: 1-6 mg/kg/day
Adult Dose (Injection):
- Insomnia: 100-320 mg IM/IV
- Convulsions: 100-320 mg IV; repeat if needed (max 600 mg/day)
- Status epilepticus: 10-20 mg/kg IV; repeat if needed
Pediatric Dose (Injection):
- Loading: 15-20 mg/kg IV over 10-15 min
- Preoperative sedation: 1-3 mg/kg IM/IV
- Anticonvulsant: 4-6 mg/kg IM/IV/day for 10 days; or 10-15 mg/kg IM/IV/day
Administration
- Oral: Take with or without food; take at a fixed time
- Injection: Administered by healthcare professional
- Maximum IV rate: 60 mg/min
Missed dose
If you miss a dose, take it as soon as you remember; skip if it's almost time for next dose; do not double the dose.
Side effects
Common Side Effects:
- Somnolence (most common)
- Agitation
- Confusion
- Hyperkinesia
- Ataxia
- CNS depression
- Nightmares
- Nervousness
- Psychiatric disturbance
- Hallucinations
- Insomnia
- Anxiety
- Dizziness
- Apnea
- Bradycardia
- Hypotension
- Nausea, vomiting, constipation
Precautions & warnings
- Tolerance and psychological/physical dependence may occur with continued use
- Caution in mentally depressed patients, suicidal tendencies, or history of drug abuse
- Caution in hepatic damage with initially reduced doses
- Pregnancy Category D; may cause fetal damage
- Small amounts excreted in breast milk
Contraindications
- Known phenobarbital sensitivity or history of latent porphyria
- Severe renal and hepatic disorders
- Severe respiratory depression, dyspnea, or airway obstruction
- Pregnancy
Drug interactions
- Alcohol or other CNS depressants: Additive CNS depressant effects
- Paracetamol overdoses: May enhance hepatotoxic potential
- CYP isoenzyme substrates (teniposide, methotrexate, antipsychotics, beta-blockers, calcium channel blockers, other anticonvulsants, chloramphenicol, cimetidine, corticosteroids, ciclosporin, doxycycline, estrogens, felbamate, griseofulvin, tacrolimus, furosemide, methadone, oral contraceptives, theophylline, TCAs, warfarin): May decrease levels/effects
- Guanfacine: May reduce effects
- Chloramphenicol, felbamate, MAOIs, valproic acid: Reduced metabolism and/or increased toxicity
- Potentially fatal: Additive sedation and/or respiratory depression with ethanol, sedatives, antidepressants, opioid analgesics, benzodiazepines, and other CNS depressants
Food interactions
Food does not affect absorption; alcohol consumption is unsafe.
Use in pregnancy
Use in Pregnancy: Pregnancy Category D; may cause fetal damage; if used during pregnancy or if pregnancy occurs, apprise of potential hazard to the fetus.
Pregnancy Category: D — always consult a doctor before taking during pregnancy.
Use in lactation
Use in Lactation: Probably unsafe; small amounts excreted in breast milk; monitor baby for sleepiness, skin rash, and feeding issues.
Pediatric use
Pediatric dosing based on age and weight; consult your doctor.
Geriatric use
Elderly patients: Dose reduction may be needed.
Renal / hepatic impairment
Renal Impairment: Caution in kidney disease; dose reduction may be needed; severe renal disease not recommended.
Hepatic Impairment: Caution in liver disease; dose reduction may be needed; severe liver disease not recommended.
Overdose effects
Toxic dose of barbiturates varies; 1 gram oral dose produces serious poisoning; death occurs after 2-10 grams. Acute overdose manifests as CNS and respiratory depression; treatment is mainly supportive with immediate hospitalization.
Storage conditions
Store below 30°C, away from light and moisture; keep out of reach of children.
Chemical structure
Phenobarbital