What is the most important information I should know about phenobarbital?

• Call your doctor immediately if you develop a fever, a sore throat, sores in your mouth, broken blood vessels under your skin, or easy bruising or bleeding. These could be early signs of a serious side effect.
  
  
• Use caution when driving, operating machinery, or performing other hazardous activities. Phenobarbital will cause drowsiness. If you experience drowsiness, avoid these activities.
  
  
• Do not drink alcohol or take other sleep medicines, antihistamines, narcotic pain relievers, or other drugs that also cause drowsiness unless your doctor approves. Dangerous sedation could result.
  
  
• Phenobarbital may decrease the effectiveness of birth control pills. Use a second method of birth control while taking phenobarbital to prevent pregnancy.

What is phenobarbital?

• Phenobarbital is in a class of drugs called barbiturates (bar bi TURE ates). Phenobarbital depresses the activity of your brain and nervous system.
  
  
• Phenobarbital is used to induce sleep, to treat insomnia (for up to 2 weeks), to prevent seizures, and to treat seizures that are already occurring.
  
  
• Phenobarbital may also be used for purposes other than those listed in this medication guide.

Who should not take phenobarbital?

• Do not take phenobarbital if you have
  
  
  
  • porphyria,
    
    
  • liver disease,
    
    
  • kidney disease, or
    
    
  • severe respiratory disease such as severe asthma or severe chronic obstructive pulmonary disorder (COPD).
  
  
• Before taking this medication, tell your doctor if you have ever had a drug or alcohol addiction in the past. Phenobarbital is habit forming, which means that you can become addicted to it.
  
  
• Phenobarbital is known to harm an unborn baby. Do not take phenobarbital if you are pregnant. However, if you take phenobarbital to control seizures, do not abruptly stop taking this medication, because a seizure could occur and this could be more harmful to an unborn baby. Talk to your doctor about treatment during pregnancy.
  
  
• Phenobarbital passes into breast milk and could affect a nursing infant. Do not take pentobarbital without first talking to your doctor if you are breast-feeding a baby.
  
  
• Phenobarbital may cause excitement, irritability, aggression, depression, or confusion--particularly in children and in adults over 60 years of age. Lower doses and close monitoring may be necessary.

How should I take phenobarbital?

• Take phenobarbital exactly as directed by your doctor. If you do not understand these directions, ask your pharmacist, nurse, or doctor to explain them to you.
  
  
• Take each dose with a full glass of water.
  
  
• To ensure that you get a correct dose, measure the liquid form of phenobarbital with a special dose-measuring spoon or cup, not with a regular tablespoon. If you do not have a dose-measuring device, ask your pharmacist where you can get one.
  
  
• To treat insomnia, phenobarbital is usually taken just before bedtime. Take your dose when you are ready to get into bed, or not long before, so that if you become sleepy, you will not fall or become confused and accidentally injure yourself. Phenobarbital should not be used for longer than 2 weeks to treat insomnia.
  
  
• To treat seizures, phenobarbital may be taken several times a day. Do not stop taking this medicine even if you are feeling well. Stopping abruptly could cause a severe seizure.
  
  
• To cause sedation, phenobarbital may be taken several times a day at regular intervals. No more than 400 mg should be taken in any one day.
  
  
• Do not increase your dosage of this medicine without the approval of your doctor. If your symptoms are not being adequately treated, talk to your doctor.
  
  
• Store phenobarbital at room temperature away from moisture and heat.

What happens if I miss a dose?

• Take the missed dose as soon as you remember. However, if it is almost time for your next regularly scheduled dose, skip the missed dose and take the next one as directed. Do not take a double dose of this medication.

What happens if I overdose?

• Seek emergency medical attention.
  
  
• Symptoms of a phenobarbital overdose include difficulty breathing, back-and-forth movements of the eyes, appearance of being drunk, fast heartbeat, low body temperature, heavy sedation, coma, and death.

What should I avoid while taking phenobarbital?

• Use caution when driving, operating machinery, or performing other hazardous activities. Phenobarbital will cause drowsiness. If you experience drowsiness, avoid these activities.
  
  
• Do not drink alcohol or take other sleep medicines, antihistamines, narcotic pain relievers, or other medicines that cause drowsiness unless your doctor approves. Dangerous sedation could result.
  
  
• Do not increase your dosage of this medicine without the approval of your doctor. If your symptoms are not being adequately treated, talk to your doctor.
  
  
• Do not take this medicine for longer than 2 weeks to treat insomnia.
  
  
• Phenobarbital may decrease the effectiveness of birth control pills. Use a second method of birth control while taking phenobarbital to prevent pregnancy.

What are the possible side effects of phenobarbital?

• If you experience any of the following serious side effects, stop taking phenobarbital and seek emergency medical attention or call your doctor immediately:
  
  
  
  • an allergic reaction (difficulty breathing; closing of your throat; swelling of your lips, tongue, or face; or hives);
    
    
  • a fever or a sore throat;
    
    
  • sores in your mouth;
    
    
  • broken blood vessels under your skin; or
    
    
  • easy bruising or bleeding.
  
  
• Other, less serious side effects may be more likely to occur. Continue to take phenobarbital and talk to your doctor if you experience
  
  
  • drowsiness or dizziness;
    
    
  • confusion;
    
    
  • agitation, irritability, or excitability;
    
    
  • nightmares, nervousness, or anxiety;
    
    
  • headache; or
    
    
  • "hangover" effect (drowsiness the day after a dose).
  
  
• Phenobarbital is habit forming, which means that you can become addicted to it. Your doctor will want to monitor how much medicine you are taking. Your dosage may have to be reduced slowly to prevent withdrawal effects.
  
  
• Side effects other than those listed here may also occur. Talk to your doctor about any side effect that seems unusual or that is especially bothersome.

What other drugs will affect phenobarbital?

• Large chronic doses of phenobarbital may cause liver damage if it is taken with acetaminophen (Tylenol, others). Tell your doctor and pharmacist if you are taking phenobarbital on a regular basis. Pain and fever reducers other than acetaminophen are available and may be more suitable choices.
  
  
• Phenobarbital may decrease the effectiveness of many drugs, including the following:
  
  
  
  • blood thinners such as warfarin (Coumadin). Blood clotting could result.
    
    
  • carbamazepine (Tegretol) and clonazepam (Klonopin). Reduced effectiveness of these medicines could lead to poor seizure control.
    
    
  • birth control pills. Breakthrough bleeding or unplanned pregnancy could result. Use of a second form of birth control is recommended.
    
    
  • steroid medicines such as hydrocortisone (Cortef, Hydrocortone), prednisone (Orasone, Deltasone), prednisolone (Prelone, Delta Cortef), methylprednisolone (Medrol), and others.
    
    
  • felodipine (Plendil), verapamil (Calan, Verelan, Isoptin), and quinidine (Cardioquin, Quinidex, Quinora, Quinaglute). Reduced effectiveness could lead to poor control of blood pressure, irregular heartbeats, or other heart conditions.
    
    
  • fenoprofen (Nalfon). Reduced effectiveness could lead to a loss of inflammation or pain control.griseofulvin (Grisactin, Fulvicin PG, Grifulvin V), and metronidazole (Flagyl, Metryl, Metizol). Reduced effectiveness could lead to recurrence or worsening of an infection.
    
    
  • theophylline (Theo-Dur, Theochron, Theolair, Slo-Bid, others). Asthma, COPD, or other respiratory conditions could grow worse.
  
  
• Other drugs may also influence the activity of phenobarbital:
  
  
  
  • Alcohol, sleep aids, antihistamines, antidepressants, and other drugs that cause tiredness or sedation may increase the drowsiness caused by phenobarbital.
    
    
  • Rifampin (Rifadin, Rimactine) may decrease the effects of phenobarbital.
  
  
• Drugs other than those listed here may also interact with phenobarbital. Talk to your doctor and pharmacist before taking any prescription or over-the-counter medicines

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The materials contained on the Epilepsy Newfoundland and Labrador website are to provide general information about epilepsy to the public. The information presented is not intended as medical or legal advice. Epilepsy Newfoundland and Labrador, its employees, board members, medical advisors, volunteers, agents and sponsors do not assume responsibility for inaccuracies or omissions or for the consequences from the use of the information obtained over this site or any links accessed through this site. Epilepsy Newfoundland and Labrador is not liable for any outcome or damages resulting from information in either a direct or indirect form. We recognize that each individual's experience of epilepsy is different. Consult your physician and/or neurologist with any questions you have.