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Generic Name: phenobarbital (FEE noe BAR bi tal)
Brand Name: Solfoton, Luminal

What is phenobarbital?

Phenobarbital is a barbiturate (bar-BIT-chur-ate). Phenobarbital slows the activity of your brain and nervous system.

Phenobarbital is used to treat or prevent seizures. Phenobarbital is also used short-term as a sedative to help you relax.

Phenobarbital may also be used for purposes not listed in this medication guide.

Important Information

You should not use phenobarbital if you have severe liver disease, severe asthma or COPD, a personal or family history of porphyria, or a history of addiction to drugs similar to phenobarbital.

Before taking this medicine

You should not take this medicine if you are allergic to phenobarbital or other barbiturates (Nembutal, Seconal, and others), or if you have:

  • severe asthma, chronic obstructive pulmonary disorder (COPD), or other breathing disorder;

  • a personal or family history of porphyria (a genetic enzyme disorder that causes symptoms affecting the skin or nervous system);

  • severe liver disease; or

  • a history of addiction to phenobarbital or similar medicines (Valium, Xanax, Ativan, and others).

To make sure phenobarbital is safe for you, tell your doctor if you have:

Follow your doctor's instructions about taking seizure medication if you are pregnant. Seizure control is very important during pregnancy, and having a seizure could harm both mother and baby. Do not start or stop taking this medicine without your doctor's advice, and tell your doctor right away if you become pregnant.

Phenobarbital can make birth control pills less effective. Ask your doctor about using a non-hormonal birth control (condom, diaphragm with spermicide) to prevent pregnancy.

It is not known whether phenobarbital passes into breast milk or if it could harm a nursing baby. Tell your doctor if you are breast-feeding a baby.

How should I take phenobarbital?

Follow all directions on your prescription label. Do not take this medicine in larger or smaller amounts or for longer than recommended.

Phenobarbital may be habit-forming. Never share phenobarbital with another person, especially someone with a history of drug abuse or addiction. Keep the medication in a place where others cannot get to it. Selling or giving away this medicine is against the law.

Do not change your phenobarbital dose without your doctor's advice. Tell your doctor if the medicine does not seem to work as well in treating your condition.

If you are taking phenobarbital to treat seizures, keep taking the medicine even if you feel fine.

Do not stop using suddenly after long-term use, or you could have unpleasant withdrawal symptoms. Ask your doctor how to safely stop using phenobarbital.

Store at room temperature away from moisture, heat, and light.

Keep track of the amount of medicine used from each new bottle. Phenobarbital is a drug of abuse and you should be aware if anyone is using your medicine improperly or without a prescription.

What happens if I miss a dose?

Take the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222. An overdose of phenobarbital can be fatal.

Overdose symptoms may include slow or shallow breathing, weak pulse, cold or clammy skin, little or no urination, pinpoint pupils, feeling cold, or fainting.

What should I avoid while taking phenobarbital?

Drinking alcohol with this medicine can cause side effects.

This medication may impair your thinking or reactions. Be careful if you drive or do anything that requires you to be alert.

Phenobarbital side effects

Phenobarbital may cause a severe allergic reaction. Stop taking phenobarbital and get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, eyes, lips, tongue, or throat.

Call your doctor at once if you have:

  • weak or shallow breathing;

  • unusual pain anywhere in your body (especially in the neck, shoulder, or arms);

  • a red blood cell disorder--pale skin, muscle weakness, diarrhea, weight loss, rapid heart rate, tongue swelling, numbness or tingling in your hands or feet, feeling short of breath; or

  • severe skin reaction--fever, sore throat, swelling in your face or tongue, burning in your eyes, skin pain followed by a red or purple skin rash that spreads (especially in the face or upper body) and causes blistering and peeling.

Side effects such as confusion, depression, or excitement may be more likely in older adults and those who are ill or debilitated.

Common side effects may include:

  • drowsiness, lack of energy;

  • dizziness or spinning sensation;

  • depressed mood;

  • feeling restless or excited (especially in children or older adults);

  • drunk feeling; or

  • "hangover" effect (drowsiness the day after taking phenobarbital).

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

See also: Side effects (in more detail)

Phenobarbital dosing information

Usual Adult Dose for Sedation:

Daytime Sedation:
30 to 120 mg orally, IM, or IV in 2 or 3 divided doses
Maximum dose: 400 mg during a 24-hour period

Preoperative Sedation:
100 to 200 mg IM 60 to 90 minutes before surgery

-Frequency of administration should be determined by the patient response.
-Parenteral administration should be reserved for situations in which oral administration is impossible/impractical.

Uses: Daytime sedation; preoperative sedation

Usual Adult Dose for Insomnia:

-Recommended dose: 100 to 200 mg orally once a day
-Maximum dose: 400 mg during a 24-hour period

-Recommended dose: 100 to 320 mg IM or IV once a day
-Maximum dose: 400 mg during a 24-hour period

-This drug may begin to lose effectiveness for inducing and maintaining sleep after 2 weeks.

Uses: Bedtime hypnosis; hypnosis

Usual Adult Dose for Seizures:

Acute Convulsions
20 to 320 mg IM or IV every 6 hours as necessary

60 to 200 mg orally per day

-Maintenance doses should be determined by clinical laboratory reference values.
-Prevention of febrile seizures may not influence the development of epilepsy.

Uses: Treatment of generalized and partial seizures; treatment/prophylaxis of febrile seizures

Usual Pediatric Dose for Seizures:

-Initial dose: 15 to 20 mg/kg orally
-Recommended dose: 3 to 6 mg/kg orally

4 to 6 mg/kg/day for 7 to 10 days or 5 to 15 mg/kg/day IM or IV

Status epilepticus:
-Initial dose: 15 to 20 mg/kg IV over 10 to 15 minutes

-Loading doses of 15 to 20 mg/kg are predicted to produce blood levels of approximately 20 mcg/mL after administration.
-Maintenance doses should be determined by clinical laboratory reference values.
-Prevention of febrile seizures may not influence the development of epilepsy.

Uses: Anticonvulsant used for the treatment of generalized and partial seizures, treatment/prophylaxis of febrile seizures, and treatment of status epilepticus.

Usual Pediatric Dose for Sedation:

1 to 3 mg/kg IM or IV

Use: Preoperative sedation

What other drugs will affect phenobarbital?

Taking this medicine with other drugs that make you sleepy or slow your breathing can cause dangerous or life-threatening side effects. Ask your doctor before taking phenobarbital with a sleeping pill, narcotic pain medicine, muscle relaxer, or medicine for anxiety, depression, or seizures.

Other drugs may interact with phenobarbital, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell each of your health care providers about all medicines you use now and any medicine you start or stop using.

Where can I get more information?

  • Your pharmacist can provide more information about phenobarbital.
  • Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.
  • Disclaimer: Every effort has been made to ensure that the information provided by Cerner Multum, Inc. ('Multum') is accurate, up-to-date, and complete, but no guarantee is made to that effect. Drug information contained herein may be time sensitive. Multum information has been compiled for use by healthcare practitioners and consumers in the United States and therefore Multum does not warrant that uses outside of the United States are appropriate, unless specifically indicated otherwise. Multum's drug information does not endorse drugs, diagnose patients or recommend therapy. Multum's drug information is an informational resource designed to assist licensed healthcare practitioners in caring for their patients and/or to serve consumers viewing this service as a supplement to, and not a substitute for, the expertise, skill, knowledge and judgment of healthcare practitioners. The absence of a warning for a given drug or drug combination in no way should be construed to indicate that the drug or drug combination is safe, effective or appropriate for any given patient. Multum does not assume any responsibility for any aspect of healthcare administered with the aid of information Multum provides. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the drugs you are taking, check with your doctor, nurse or pharmacist.

Copyright 1996-2012 Cerner Multum, Inc. Version: 8.01.

Date modified: January 03, 2018
Last reviewed: March 18, 2016