Uses
What is phenobarbital used for?
Phenobarbital is commonly used as a sedative (to cause drowsiness) or to control certain types of seizures.
Phenobarbital may also be used for other conditions as determined by your healthcare provider.
How does phenobarbital work (mechanism of action)?
Phenobarbital may work by mimicking a natural chemical in your brain called GABA, which helps calm brain activity. This reduces seizures and makes you feel sleepy.
How is phenobarbital supplied (dosage forms)?
Phenobarbital is available in the following dosage forms that are taken by mouth.
- 20 mg/5 mL oral elixir
- 15 mg, 16.2 mg, 30 mg, 32.4 mg, 60 mg, 64.8 mg, 97.2 mg, 100 mg oral tablets
Phenobarbital is also available in injectable forms.
How should I store phenobarbital?
Tablets or Liquid. Phenobarbital tablets and liquid should be stored at room temperature, between 68 F to 77 F (20 C to 25 C). It can be exposed to temperatures between 59 F to 86 F (15 C to 30 C) for shorter periods of time, such as when transporting it. Store tightly closed, away from direct sunlight, in a cool, dry place.
Injection. Phenobarbital for injection is usually given by a healthcare provider in a hospital or clinic. You will not store it at home.
Side Effects
What are the most common side effects of phenobarbital?
The most common side effects of phenobarbital are listed below. Tell your healthcare provider if you have any of these side effects that bother you.
- Drowsiness or sleepiness
- Breathing problems (see below)
- Problems taking in breast milk (infants)
- Low blood pressure
There may be other side effects of phenobarbital that are not listed here. Contact your healthcare provider if you think you are having a side effect of a medicine. In the U.S., you can report side effects to the FDA at www.fda.gov/medwatch or by calling 800-FDA-1088. In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.
What are the serious side effects of phenobarbital?
While less common, the most serious side effects of phenobarbital are described below, along with what to do if they happen.
Severe Allergic Reactions. Phenobarbital may cause allergic reactions, including a specific type of allergic reaction called DRESS. DRESS stands for Drug Reaction with Eosinophilia and Systemic Symptoms. It is also sometimes called multi-organ hypersensitivity. This is a reaction that can affect multiple parts of the body including your liver, kidneys, and heart. Stop taking the medicine and get help right away if you have any of the following symptoms of a serious allergic reaction.
- Breathing problems or wheezing
- Racing heart
- Itching, skin rash, or pale red bumps on the skin called hives
- Fever or general ill feeling
- Swollen lymph nodes
- Swelling of the face, lips, mouth, tongue, or throat
- Shortness of breath, trouble swallowing, or throat tightness
- Swelling in your feet, ankles, or legs
- Nausea or vomiting
- Dizziness, feeling lightheaded, or fainting
- Stomach cramps
- Joint pain
- Dark-colored pee
- Your skin or the whites of your eyes turning yellowish in color (also called jaundice)
Infusion Site Reactions. Injectable phenobarbital can cause reactions that can be serious when it is given to you. The infusion may need to be slowed or stopped if you have these reactions. Tell your healthcare provider right away if you notice any of the following symptoms near the injection site.
- Pain or swelling
- Color or temperature changes
Severe Skin Reactions. Phenobarbital can cause severe skin reactions called Stevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN) that can lead to death if not treated. If you develop a rash, stop phenobarbital, and call your healthcare provider right away. Get emergency help right away if you have any of the following symptoms of SJS or TEN.
- Painful red or purple skin that looks burned and peels off
- Flat red rash or blisters on your skin, mouth, nose, and genitals
- Red, painful, watery eyes
Suicidal Thoughts and Actions. Phenobarbital may cause suicidal thoughts or actions in a small number of people. If you are about to harm yourself, call 911 or call or text 988, the Suicide & Crisis Lifeline. Call your healthcare provider right away if you have any of the following symptoms.
- New or increased thoughts of suicide or death
- Suicide attempt
- New or increased feelings of anxiety, depression, or other unusual changes in mood or behavior
Central Nervous System (CNS) Depression. Phenobarbital may slow down your central nervous system (CNS), which controls many vital functions throughout the body. Call your healthcare provider right away if you have any of the following symptoms of CNS depression.
- Confusion
- Excessive sleepiness or trouble staying awake
- Memory problems
- Slow or shallow breathing
- Slowed response or reaction time
- Slurred speech
Breathing Problems. Phenobarbital may cause slow or shallow breathing, especially if you have breathing problems from another condition or take other medicines that can slow your breathing. Tell your healthcare provider if you develop severe sleepiness or trouble breathing, especially when you start phenobarbital or when your dose is increased. Get emergency help if you have any of the following symptoms.
- Changes in the color of your skin, including bluish color to your lips and fingernails
- Confusion
- Shortness of breath
- Feeling dizzy, lightheaded, or fainting
- Changes in your heart rate or rhythm, such as a fast, slow, pounding or skipping heartbeat
- Slow or shallow breathing
- Excessive sleepiness or trouble staying awake
Dependence and Withdrawal Reactions. Phenobarbital can cause physical dependence, which means your body relies on the medicine to function properly. If you stop phenobarbital suddenly, it could lead to withdrawal symptoms, which may be life-threatening. Do not stop taking phenobarbital without talking with your healthcare provider. Your healthcare provider can tell you how to stop phenobarbital to reduce the risk of withdrawal reactions. Call your healthcare provider right away or go to the nearest emergency room if you have any of the following serious symptoms.
- Unusual movements, responses, or expressions
- Seizures
- Sudden and severe mental or nervous system changes
- Seeing or hearing things that others do not see or hear, also called hallucinations
- An extreme increase in activity or talking
- Losing touch with reality
Heart Rhythm Changes. Phenobarbital may cause a rare, dangerous heart rhythm problem called QT prolongation and torsade de pointes. Some people have a higher risk of this, including people who are older, have other people in their family who have had these conditions, have low potassium or magnesium levels, or who take some medicines for other heart rhythm problems. Tell your healthcare provider right away if you faint or have changes in your heart rate or rhythm, such as a fast or skipping heartbeat.
Warnings & Precautions
Who should not use phenobarbital?
Allergies to Ingredients. People who are allergic to any of the following should not take phenobarbital.
- Phenobarbital
- Luminal
- Sezaby
- Any other medicine known as a barbiturate
- Any of the ingredients in the specific product dispensed
Your pharmacist can tell you all of the ingredients in the specific phenobarbital products they stock.
Porphyria. Phenobarbital should not be used if you have porphyria. Porphyria is a genetic disorder that most often affects your skin. Tell your healthcare provider if you have porphyria.
Liver Problems. Phenobarbital should not be used if your liver is not working as well as it should be. If there is a concern about the health of your liver, your healthcare provider may do tests to determine if it is working well enough to take this medicine.
Breathing Problems. Phenobarbital should not be used if you have lung or breathing problems with shortness of breath. Tell your healthcare provider if you have any breathing problems.
What should I know about phenobarbital before using it?
Do not take phenobarbital unless it has been prescribed to you by a healthcare provider. Take it as prescribed.
Do not share phenobarbital with other people, even if they have the same condition as you. It may harm them.
Keep phenobarbital out of the reach of children. Phenobarbital is a controlled substance because it can be misused or lead to dependence. Store phenobarbital in a safe place to protect it from theft. It is illegal to sell or give away this medicine.
Phenobarbital can affect your alertness or coordination. Do not drive or do other activities that require alertness or coordination until you know how phenobarbital affects you.
Do not stop taking phenobarbital without talking to your healthcare provider. Stopping phenobarbital suddenly can cause withdrawal symptoms which can be life threatening. If you need to stop taking phenobarbital, your healthcare provider will give you instructions on how to stop the medicine.
Phenobarbital may decrease how well your birth control medicine works. You may need to use a backup method or another method of birth control while you are taking phenobarbital to avoid getting pregnant. Talk with your healthcare provider about your birth control options.
Children or people who are 65 or older can be at greater risk for some side effects from phenobarbital. Talk to your healthcare provider about your risks if you are in one of these age groups.
What should I tell my healthcare provider before using phenobarbital?
Tell your healthcare provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are taking. This will help them determine if phenobarbital is right for you.
In particular, make sure that you discuss any of the following.
Current and Past Health Conditions. Tell your healthcare provider if you have any of the following.
- Mental health conditions, such as depression or mood problems
- Suicidal thoughts or actions
- Drug or alcohol abuse
- Pain
Other Medicines and Supplements. Phenobarbital may interact with other medicines and supplements. Before taking phenobarbital, tell your healthcare provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are taking. See the Interactions section for more details.
Pregnancy. Phenobarbital may cause harm to an unborn baby. Tell your healthcare provider if you are or plan to become pregnant. Your healthcare provider will advise you if you should take phenobarbital while you are pregnant or trying to get pregnant. If you become pregnant while taking phenobarbital, you can register for the North American Antiepileptic Drug Pregnancy Registry by calling 888-233-2334 or at www.aedpregnancyregistry.org. This registry collects safety information about the use of medicines to control seizures during pregnancy.
Breastfeeding. Phenobarbital passes into breast milk. Tell your healthcare provider if you are breastfeeding or plan to breastfeed. Your healthcare provider will advise you if you should take phenobarbital while breastfeeding.
Interactions
Does phenobarbital interact with foods or drinks?
There are no known interactions between phenobarbital and foods or drinks.
Avoid drinking alcohol while taking phenobarbital. It is unknown if drinking alcohol will affect phenobarbital. The risk of dizziness or sleepiness may be increased if you drink alcohol while taking phenobarbital.
Does phenobarbital interact with other medicines (drug interactions)?
Always tell your healthcare provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.
In particular, make sure that you discuss if you are using any of the following before taking phenobarbital.
- A medicine that causes dizziness and sleepiness, such as prescription pain medicines, allergy medicines, sleep medicines, and medicines for anxiety
- An opioid, such as oxycodone, morphine, codeine, or fentanyl, which is a medicine used for certain types of pain
- A corticosteroid, which is a medicine for certain inflammatory conditions
- A birth control pill, patch, vaginal ring, implant, injection, or intrauterine device (IUD)
- Warfarin, which is a blood thinner
- Griseofulvin, which is used for fungal infections
- Doxycycline, which is a medicine used to treat infections or other conditions
- Phenytoin (Dilantin, Phenytek, and others), which is a medicine to control seizures
- A monoamine oxidase inhibitor (MAOI), which is a medicine usually used for depression or Parkinson’s disease
- Medicines that can cause QT prolongation, which is a potentially dangerous heart rhythm problem
Many other medicines may alter the blood levels of phenobarbital, and vice versa. Tell your healthcare provider about all medicines that you take or have recently taken.
This may not be a complete list of medicines that can interact with phenobarbital. Always check with your healthcare provider.
Overdose/Missed Dose
What should I do if I accidentally use too much phenobarbital?
If you or someone else has used too much phenobarbital, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.
What should I do if I miss a dose of phenobarbital?
If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and only take the next dose. Do not take double or extra doses.
Are you currently using Phenobarbital?
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