WHY is this medicine prescribed?
Phenobarbital is used to control seizures. Phenobarbital is also used to relieve anxiety. It is also used to prevent withdrawal symptoms in people who are dependent ('addicted'; feel a need to continue taking the medication) on another barbiturate medication and are going to stop taking the medication. Phenobarbital is in a class of medications called barbiturates. It works by slowing activity in the brain.
HOW should this medicine be used?
Phenobarbital comes as a tablet and an elixir (liquid) to take by mouth. It is usually taken one to three times a day. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take phenobarbital exactly as directed.
If you take phenobarbital for a long time, it may not control your symptoms as well as it did at the beginning of your treatment. Talk to your doctor about how you are feeling during your treatment.
Phenobarbital can be habit-forming. Do not take a larger dose, take it more often, or take it for a longer time than prescribed by your doctor.
Do not stop taking phenobarbital without talking to your doctor. If you suddenly stop taking phenobarbital, you may experience withdrawal symptoms such as anxiety, muscle twitching, uncontrollable shaking of a part of the body, weakness, dizziness, changes in vision, nausea, vomiting, seizures, confusion,difficulty falling asleep or staying asleep, or dizziness or fainting when getting up from a lying position. Your doctor will probably decrease your dose gradually.
Are there OTHER USES for this medicine?
This medication may be prescribed for other uses. Ask your doctor or pharmacist for more information.
What SPECIAL PRECAUTIONS should I follow?
Before taking phenobarbital,
- tell your doctor and pharmacist if you are allergic to phenobarbital; other barbiturates such as amobarbital (Amytal), butabarbital (Butisol), pentobarbital, and secobarbital (Seconal); any other medications, or any of the ingredients in phenobarbital tablets or liquid. Ask your doctor or pharmacist for a list of the ingredients.
- tell your doctor and pharmacist what prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Be sure to mention any of the following: anticoagulants ('blood thinners') such as warfarin (Coumadin); disulfiram (Antabuse); doxycycline (Vibramycin); griseofulvin (Fulvicin); hormone replacement therapy (HRT); monoamine oxidase (MAO) inhibitors such as isocarboxazid (Marplan), phenelzine (Nardil), seligiline (Eldepryl, Emsam, Zelapar) , or tranylcypromine (Parnate); medications for anxiety, depression, pain, asthma, colds, or allergies; certain medications for seizures such as phenytoin (Dilantin) and valproate (Depakene); oral steroids such as dexamethasone (Decadron, Dexone), methylprednisolone (Medrol), and prednisone (Deltasone);sedatives; sleeping pills; and tranquilizers. Your doctor may need to change the doses of your medications or monitor you more carefully for side effects.
- tell your doctor if you have or have ever had porphyria (condition in which certain natural substances build up in the body and may cause stomach pain, changes in thinking and behavior, and other symptoms); any condition that causes shortness of breath or difficulty breathing; or liver disease. Your doctor will probably tell you not to take phenobarbital.
- tell your doctor if you drink or have ever drunk large amounts of alcohol, used street drugs, or overused prescription medications; if you have pain now or have any condition that causes you ongoing pain; if you have ever thought about harming or killing yourself or planned or tried to do so; and if you have or have ever had depression, any condition that affects your adrenal gland (small gland next to the kidney that produces important natural substances), or kidney disease.
- tell your doctor if you are pregnant, plan to become pregnant, or are breastfeeding. If you become pregnant while taking phenobarbital, call your doctor. Phenobarbital may harm the fetus.
- talk to your doctor about the risks and benefits of taking phenobarbital if you are 65 years of age or older. Older adults should not usually take phenobarbital because it is not as safe or effective as other medications that can be used to treat the same condition.
- you should know that phenobarbital may decrease the effectiveness of hormonal contraceptives (birth control pills, patches, rings, injections, implants, or intrauterine devices). Talk to your doctor about methods of birth control that will work for you while you are taking phenobarbital. Tell your doctor if you have a missed period or think you may be pregnant while you are taking phenobarbital.
- if you are having surgery, including dental surgery, tell the doctor or dentist that you are taking phenobarbital.
- you should know that this medication may make you drowsy. Do not drive a car or operate machinery until you know how this medication affects you.
- avoid drinking alcohol during your treatment with phenobarbital. Alcohol can make the side effects of phenobarbital worse.
What SPECIAL DIETARY instructions should I follow?
Unless your doctor tells you otherwise, continue your normal diet.
What should I do IF I FORGET to take a dose?
Take the missed dose as soon as you remember it. However, if it is almost time for your next dose, skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one.
What SIDE EFFECTS can this medicine cause?
Phenobarbital may cause side effects. Call your doctor if any of the following symptoms are severe or do not go away:
- excitement or increased activity (especially in children)
Some side effects can be serious. If you experience any of the following symptoms, call your doctor immediately:
- slowed breathing or difficulty breathing
- swelling of the eyes, lips, or cheeks
- blistering or peeling skin
If you experience a serious side effect, you or your doctor may send a report to the Food and Drug Administration's (FDA) MedWatch Adverse Event Reporting program online ( Web Site ) or by phone (1-800-332-1088).
What should I know about STORAGE and DISPOSAL of this medication?
Keep this medication in the container it came in, tightly closed, and out of reach of children. Store it at room temperature and away from excess heat and moisture (not in the bathroom).
It is important to keep all medication out of sight and reach of children as many containers (such as weekly pill minders and those for eye drops, creams, patches, and inhalers) are not child-resistant and young children can open them easily. To protect young children from poisoning, always lock safety caps and immediately place the medication in a safe location – one that is up and away and out of their sight and reach. Web Site
Unneeded medications should be disposed of in special ways to ensure that pets, children, and other people cannot consume them. However, you should not flush this medication down the toilet. Instead, the best way to dispose of your medication is through a medicine take-back program. Talk to your pharmacist or contact your local garbage/recycling department to learn about take-back programs in your community. See the FDA's Safe Disposal of Medicines website ( Web Site) for more information if you do not have access to a take-back program.
What should I do in case of OVERDOSE?
In case of overdose, call the poison control helpline at 1-800-222-1222. Information is also available online at Web Site. If the victim has collapsed, had a seizure, has trouble breathing, or can't be awakened, immediately call emergency services at 911.
Symptoms of overdose may include the following:
- uncontrollable movements of the eyes
- loss of coordination
- slowed breathing
- drop in body temperature
What OTHER INFORMATION should I know?
Keep all appointments with your doctor and the laboratory. Your doctor will order certain lab tests to check your response to phenobarbital.
Do not let anyone else take your medication. Ask your pharmacist any questions you have about refilling your prescription.
It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.
AHFS® Consumer Medication Information. © Copyright, The American Society of Health-System Pharmacists, Inc., 7272 Wisconsin Avenue, Bethesda, Maryland. All Rights Reserved. Duplication for commercial use must be authorized by ASHP.
Selected Revisions: September 15, 2018.