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Phenobarbital

Last reviewed on RxList: 1/17/2017
Phenobarbital Side Effects Center

Last reviewed on RxList 9/23/2016

Phenobarbital (Brand Name: Solfoton) is a barbiturate used to treat or prevent seizures. Phenobarbital is also used short-term to treat insomnia, or as a sedative before surgery. Phenobarbital is available in generic form. Common side effects of phenobarbital include:

  • dizziness,
  • drowsiness,
  • problems with memory or concentration,
  • excitation,
  • irritability,
  • aggression,
  • confusion (especially in children or older adults);
  • loss of balance or coordination,
  • headache,
  • tiredness,
  • loss of appetite,
  • nausea,
  • vomiting, or
  • constipation as your body adjusts to the medication.
  • You may also experience a "hangover" effect (drowsiness the day after a dose) after taking phenobarbital.

Dosing of Phenobarbital depends on its use. Phenobarbital may interact with doxycycline, other seizure medications, MAO inhibitors, griseofulvin, birth control pills or estrogen hormone replacement, or steroids. Tell your doctor all medications you use. Phenobarbital is not recommended for use during pregnancy. It may harm a fetus. Since untreated seizures are a serious condition that can harm both a pregnant woman and the fetus, do not stop taking this medication unless directed by your doctor. Hormonal birth control may not work if taken with this medication. Discuss birth control with your doctor. Phenobarbital may lower folic acid and vitamin K levels, increasing the risk of spinal cord defects. Infants born to mothers who have use this medication during pregnancy may also have symptoms such as fussiness, shaking, or bleeding. Tell the doctor if you notice symptoms in your newborn. This medication passes into breast milk and may cause excessive sleepiness or feeding problems in the nursing infant. Consult your doctor before breastfeeding. Withdrawal symptoms may occur if you abruptly stop taking this drug.

Our Phenobarbital Side Effects Drug Center provides a comprehensive view of available drug information on the potential side effects when taking this medication.

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.

Phenobarbital Consumer Information

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

Call your doctor at once if you have any of these serious side effects:

  • restless muscle movements in your eyes, tongue, jaw, or neck;
  • slow heartbeat, shallow breathing;
  • feeling light-headed, fainting;
  • a fever or a sore throat;
  • sores in your mouth;
  • easy bruising or bleeding; or
  • broken blood vessels under your skin.

Less serious side effects may include:

  • drowsiness or dizziness;
  • problems with memory or concentration;
  • excitement, irritability, aggression, or confusion (especially in children or older adults);
  • loss of balance or coordination;
  • nausea, constipation;
  • headache; or
  • "hangover" effect (drowsiness the day after a dose).

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.

Read the entire detailed patient monograph for Phenobarbital (Phenobarbital)

Phenobarbital Professional Information

SIDE EFFECTS

The following adverse reactions and their incidence were compiled from surveillance of thousands of hospitalized patients.

More than 1 in 100 patients:
The most common adverse reaction estimated to occur at a rate of 1 to 3 patients per 100 is:
Less than 1 in 100 patients:
Adverse reactions estimated to occur at a rate of less than 1 in 100 patients listed below, grouped by organ system, and by decreasing order of occurrence are:

DRUG ABUSE AND DEPENDENCE

Phenobarbital may be habit forming:
Tolerance, psychological dependence, and physical dependence may occur especially following prolonged use of high doses of phenobarbital. As tolerance to phenobarbital develops, the amount needed to maintain the same level of intoxication increases; tolerance to a fatal dosage, however, does not increase more than two-fold. As this occurs, the margin between an intoxicating dosage and fatal dosage becomes smaller.

Symptoms of acute intoxication with phenobarbital include unsteady gait, slurred speech, and sustained nystagmus. Mental signs of chronic intoxication include confusion, poor judgment, irritability, insomnia, and somatic complaints.

Symptoms of phenobarbital dependence are similar to those of chronic alcoholism. If an individual appears to be intoxicated with alcohol to a degree that is radically disproportionate to the amount of alcohol in his or her blood, the use of barbiturates should be suspected. The lethal dose of a barbiturate is far less if alcohol is also ingested. The symptoms of phenobarbital withdrawal can be severe and may cause death. Minor withdrawal symptoms may appear 8 to 12 hours after the last dose of phenobarbital. These symptoms usually appear in the following order: anxiety, muscle twitching, tremor of hands and fingers, progressive weakness, dizziness, distortion in visual perception, nausea, vomiting, insomnia, and orthostatic hypotension. Major withdrawal symptoms (convulsions and delirium) may occur within 16 hours and last up to 5 days after abrupt cessation of this drug. Intensity of withdrawal symptoms gradually declines over a period of approximately 15 days. Individuals susceptible to phenobarbital abuse and dependence include alcoholics and opiate abusers, as well as other sedative- hypnotic and amphetamine abusers.

Drug dependence on phenobarbital arises from repeated administration of the barbiturate or an agent with barbiturate- like effect on a continuous basis, generally in amounts exceeding therapeutic dose levels. The characteristics of drug dependence on phenobarbital include: (a) a strong desire or need to continue taking the drug, (b) a tendency to increase the dose, (c) a psychic dependence on the effects of the drug related to subjective and individual appreciation of those effects, and (d) a physical dependence on the effects of the drug requiring its presence for maintenance of homeostasis and resulting in a definite, characteristic, and self-limited abstinence syndrome when the drug is withdrawn.

Treatment of phenobarbital dependence consists of cautious and gradual withdrawal of the drug. One method involves substituting a 30 mg dose of phenobarbital for each 100 to 200 mg dose that the patient has been taking. The total daily amount of phenobarbital is then administered in 3 to 4 divided doses, not to exceed 600 mg daily. Should signs of withdrawal occur on the first day of treatment, a loading dose of 100 to 200 mg of phenobarbital may be administered IM in addition to the oral dose. After stabilization on phenobarbital, the total daily dose is decreased by 30 mg a day as long as withdrawal is proceeding smoothly. A modification of this regimen involves initiating treatment at the patient's regular dosage level and decreasing the daily dosage by 10 percent if tolerated by the patient.

Infants physically dependent on phenobarbital may be given a lower dose of phenobarbital at 3 to 10 mg/kg/day. After withdrawal symptoms (hyperactivity, disturbed sleep, tremors, hyperreflexia) are relieved, the dosage of phenobarbital should be gradually decreased and completely withdrawn over a 2-week period.

Read the entire FDA prescribing information for Phenobarbital (Phenobarbital)

Related Resources for Phenobarbital

Read the Phenobarbital User Reviews »

© Phenobarbital Patient Information is supplied by Cerner Multum, Inc. and Phenobarbital Consumer information is supplied by First Databank, Inc., used under license and subject to their respective copyrights.

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