Reviewed on 9/2/2021

What Is Phenobarbital and How Does It Work?

Phenobarbital is used alone or with other medications to control seizures. Controlling and reducing seizures lets you do more of your normal daily activities, reduces your risk of harm when you lose consciousness, and lessens your risk for a possibly life-threatening condition of frequent, repeated seizures.

  • Phenobarbital belongs to a class of drugs known as barbiturate anticonvulsants/hypnotics. It works by controlling the abnormal electrical activity in the brain that occurs during a seizure.
  • Phenobarbital is also used for a short time (usually no more than 2 weeks) to help calm you or help you sleep during periods of anxiety.
  • It works by affecting certain parts of the brain to cause calming.

What Are Dosages of Phenobarbital?

Dosages of Phenobarbital:

Dosage Forms and Strengths

Tablet: Schedule IV

  • 15 mg
  • 16 mg
  • 30 mg
  • 32 mg
  • 60 mg
  • 64.8 mg
  • 65 mg
  • 100 mg

Elixir: Schedule IV

  • 20 mg/5mL

Injectable solution: Schedule IV

  • 30 mg/mL
  • 60 mg/mL
  • 65 mg/mL
  • 130 mg/mL
Dosage Considerations – Should be Given as Follows:

Status Epilepticus

  • Typically used after benzodiazepines and phenytoin fail to abort status epilepticus
  • Adult: 15-18 mg/kg intravenous (IV) loading dose infused at 25-60 mg/min; prepare to support ventilation; may repeat in 20-minute intervals as needed; not to exceed 30 mg/kg
  • Infants and children: 15-20 mg/kg IV infused at a rate not to exceed 2 mg/kg/min; not to exceed 1000 mg/dose
  • Children under 60 kg: IV rate at less than 30 mg/min
  • May repeat with 5-10 mg/kg bolus dose after 15-30 min as needed; not to exceed the cumulative dose of 40 mg/kg


  • All types of seizure disorders, including partial, tonic-clonic, and myoclonic seizures
  • Adult: 1-3 mg/kg/day oral/intravenous (IV) in 1-2 divided doses initially; adjust accordingly to maintain within the therapeutic serum concentration range
  • Neonates (less than 28 days): 3-5 mg/kg/day intravenously (IV)/orally in 1-2 divided doses
  • Infants: 5-6 mg/kg/day intravenously (IV)/orally in 1-2 divided doses
  • Children 1-5 years: 6-8 mg/kg/day intravenously (IV)/orally in 1-2 divided doses
  • Children 6-12 years: 4-6 mg/kg/day intravenously (IV)/orally in 1-2 divided doses
  • Children over 12 years: 1-3 mg/kg/day intravenously (IV)/orally in 1-2 divided doses, OR 50-100 mg two or three times daily


  • Adult: 30-120 mg/day orally divided two or three times daily; do not exceed 400 mg/day
  • Pediatric: 2 mg/kg orally three times daily


  • Adult: 100-320 mg/day orally/intravenously/intramuscularly; do not administer for more than 2 weeks
  • Pediatric: 3-5 mg/kg orally at bedtime


  • 100-200 mg orally at bedtime; do not exceed 400 mg/day

Preoperative Sedation, Pediatric

  • 1-3 mg/kg orally/intravenously/intramuscularly 1-1.5 hours before procedure

Hyperbilirubinemia (Off-label), Pediatric

  • Neonates: 5 mg/kg/day orally/intravenously (IV) once/day, OR divided every 12 hours for 3-6 days following birth
  • Children under 12 years (chronic cholestasis): 1.5-4 mg/kg orally every 12 hours

Dosing Considerations

  • Antiepileptic therapeutic concentration range: 10-40 mcg/L (43-172 micromoles/L)
  • Long half-life permits once-daily dosing, if tolerated, for seizures; single daily dosing at bedtime recommended because of sedation
  • Children under 6 years: Potential toxic dose 8 mg/kg
  • Pediatric: Antiepileptic therapeutic concentration range: 15-30 mcg/L (43-129 micromoles/L)


What Is Epilepsy? Symptoms, Causes, and Treatments See Slideshow

What Are Side Effects Associated with Using Phenobarbital?

Common side effects of phenobarbital include:

  • Aggression
  • Dizziness
  • Drowsiness
  • Excitation
  • Fatigue
  • Headache
  • Irritability
  • Loss of appetite
  • Loss of balance or coordination
  • Loss of control of bodily movements
  • Numbness and tingling
  • Problems with memory or concentration
  • Repetitive, uncontrolled eye movements
  • Respiratory depression (IV)
  • Restlessness
  • Slurred or slow speech
  • Spinning sensation (vertigo)
  • Tiredness
  • Geriatric patients: Excitement, confusion, depression
  • Pediatric patients: Paradoxical excitement/hyperactivity

Fewer side effects of phenobarbital include:

  • Mental dullness
  • Constipation
  • Diarrhea
  • Nausea
  • Vomiting
  • Megaloblastic (folate-deficiency) anemia

Uncommon side effects of phenobarbital include:

Rare side effects of phenobarbital include:

This is not a complete list of side effects and other serious side effects may occur. Call your doctor for information and medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

What Other Drugs Interact with Phenobarbital?

If your doctor has directed you to use this medication for your condition, your doctor or pharmacist may already be aware of any possible drug interactions or side effects and may be monitoring you for them. Do not start, stop, or change the dosage of this medicine or any medicine before getting further information from your doctor, healthcare provider, or pharmacist first.

  • Phenobarbital has severe interactions with at least 29 different drugs.
  • Phenobarbital has serious interactions with at least 89 different drugs.
  • Phenobarbital has moderate interactions with at least 393 different drugs.
  • Phenobarbital has mild interactions with at least 166 different drugs.

This document does not contain all possible interactions. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you, and share the list with your doctor and pharmacist. Check with your physician if you have health questions or concerns.

What Are Warnings and Precautions for Phenobarbital?


This medication contains phenobarbital. Do not take if you are allergic to phenobarbital or any ingredients contained in this drug.

Keep out of reach of children. In case of overdose, get medical help or contact a Poison Control Center immediately.


Effects of Drug Abuse

  • No information available

Short-Term Effects

  • See "What Are Side Effects Associated with Using Phenobarbital?"

Long-Term Effects

  • See "What Are Side Effects Associated with Using Phenobarbital?"


  • A commercial injection is highly alkaline and may cause tissue necrosis if given subcutaneously (SC) or if it extravasates (it happens, treat with an application of moist heat and injection of 0.5% procaine).
  • May render oral contraceptive pills ineffective.

Pregnancy and Lactation

  • Use phenobarbital during pregnancy only in LIFE-THREATENING emergencies when no safer drug is available. There is positive evidence of human fetal risk.


See Images
Medscape. Phenobarbital.
RxList. Phenobarbital Side Effects Drug Center.

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