Phenytoin

This information from Lexicomp^® explains what you need to know about this medication, including what it’s used for, how to take it, its side effects, and when to call your healthcare provider.

Brand Names: US

Dilantin; Dilantin Infatabs; Dilantin-125; Phenytek; Phenytoin Infatabs

Brand Names: Canada

Dilantin; Dilantin Infatabs; Dilantin-125; Dilantin-30; TARO-Phenytoin; Tremytoine

What is this drug used for?

• It is used to help control certain kinds of seizures.

What do I need to tell my doctor BEFORE I take this drug?

• If you are allergic to this drug; any part of this drug; or any other drugs, foods, or substances. Tell your doctor about the allergy and what signs you had.
• If you are taking delavirdine.
• If you have had liver problems in the past while taking this drug.
• If you have a slow heartbeat, heart block, or other heartbeat that is not normal.

This is not a list of all drugs or health problems that interact with this drug.

This drug interacts with many other drugs. The chance of severe, life-threatening, or deadly side effects may be raised. Tell your doctor and pharmacist about all of your drugs (prescription or OTC, natural products, vitamins) and health problems. You must check to make sure that it is safe for you to take this drug with all of your drugs and health problems. Do not start, stop, or change the dose of any drug without checking with your doctor.

What are some things I need to know or do while I take this drug?

• Tell all of your health care providers that you take this drug. This includes your doctors, nurses, pharmacists, and dentists.
• Wear disease medical alert ID (identification).
• Have your blood work and other lab tests checked as you have been told by your doctor.
• Have the level of phenytoin in your blood checked as you have been told by your doctor. If the level is too high, some side effects may happen. This includes a type of brain problem that may not go back to normal. Talk with your doctor.
• Do not stop taking this drug all of a sudden without calling your doctor. You may have a greater risk of seizures. If you need to stop this drug, you will want to slowly stop it as ordered by your doctor.
• Follow laws about driving with a seizure problem.
• Avoid driving and doing other tasks or actions that call for you to be alert until you see how this drug affects you.
• This drug may affect certain lab tests. Tell all of your health care providers and lab workers that you take this drug.
• If you have high blood sugar (diabetes), you will need to watch your blood sugar closely.
• Talk with your doctor before you use alcohol, marijuana or other forms of cannabis, or prescription or OTC drugs that may slow your actions.
• Take good care of your teeth. See a dentist often.
• If seizures are different or worse after starting this drug, talk with the doctor.
• People with a certain gene (HLA-B*1502) have a higher chance of severe and sometimes deadly skin reactions with this drug. This gene is more common in people of Asian descent, including South Asian Indian people. The chance may also be higher in people with a gene type called CYP2C9*3. If you have questions, talk with the doctor.
• This drug may cause weak bones. This may happen more often if used for a long time. This may raise the chance of broken bones. Call your doctor right away if you have bone pain.
• If you are 65 or older, use this drug with care. You could have more side effects.
• Birth control pills and other hormone-based birth control may not work as well to prevent pregnancy. Use some other kind of birth control also like a condom when taking this drug.
• This drug may cause harm to the unborn baby if you take it while you are pregnant. If you are pregnant or you get pregnant while taking this drug, call your doctor right away.
• A bleeding problem that can be life-threatening may happen in newborns if you took this drug during pregnancy.
• Tell your doctor if you are breast-feeding. You will need to talk about any risks to your baby.

What are some side effects that I need to call my doctor about right away?

WARNING/CAUTION: Even though it may be rare, some people may have very bad and sometimes deadly side effects when taking a drug. Tell your doctor or get medical help right away if you have any of the following signs or symptoms that may be related to a very bad side effect:

All products:

• Signs of an allergic reaction, like rash; hives; itching; red, swollen, blistered, or peeling skin with or without fever; wheezing; tightness in the chest or throat; trouble breathing, swallowing, or talking; unusual hoarseness; or swelling of the mouth, face, lips, tongue, or throat.
• Signs of high blood sugar like confusion, feeling sleepy, unusual thirst or hunger, passing urine more often, flushing, fast breathing, or breath that smells like fruit.
• Trouble walking.
• Feeling confused.
• Slurred speech.
• Swollen or sore gums.
• Very bad muscle pain.
• Trouble controlling body movements, twitching, change in balance, trouble swallowing or speaking.
• A burning, numbness, or tingling feeling that is not normal.
• Not able to control eye movements.
• Shakiness.
• Heart problems like slow heartbeat have happened with this drug. Call your doctor right away if you have any signs of heart problems like dizziness or passing out, chest pain or pressure, tiredness, or abnormal heartbeat.
• Severe skin reactions have happened with this drug. These have included Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), and other severe skin reactions. Sometimes these have been deadly. Get medical help right away if you have signs like red, swollen, blistered, or peeling skin; other skin irritation (with or without fever); red or irritated eyes; or sores in your mouth, throat, nose, or eyes.
• Like other drugs that may be used for seizures, this drug may rarely raise the risk of suicidal thoughts or actions. The risk may be higher in people who have had suicidal thoughts or actions in the past. Call the doctor right away about any new or worse signs like depression; feeling nervous, restless, or grouchy; panic attacks; or other changes in mood or behavior. Call the doctor right away if any suicidal thoughts or actions occur.
• A severe and sometimes deadly effect has happened in people taking drugs for seizures like this drug. Call your doctor right away if you have swollen glands; fever; rash; painful sores in the mouth or around the eyes; chest pain; signs of kidney problems like unable to pass urine or change in the amount of urine passed; or signs of liver problems like dark urine, tiredness, decreased appetite, upset stomach or stomach pain, light-colored stools, throwing up, or yellow skin or eyes.
• Rarely, certain blood problems have happened with this drug. This can lead to bleeding problems or infections. Sometimes, these have been deadly. Tell your doctor right away if you have signs of infection like fever, chills, very bad sore throat, ear or sinus pain, cough, more sputum or change in color of sputum, pain with passing urine, mouth sores, or a wound that will not heal. Tell your doctor right away if you have any unexplained bruising or bleeding, pale skin, or if you feel very tired or weak.

Injection:

• Change in skin color to black or purple.
• This drug may cause tissue damage if the drug leaks from the vein. Tell your nurse if you have any redness, burning, pain, swelling, blisters, skin sores, or leaking of fluid where the drug is going into your body.

What are some other side effects of this drug?

All drugs may cause side effects. However, many people have no side effects or only have minor side effects. Call your doctor or get medical help if any of these side effects or any other side effects bother you or do not go away:

• Feeling dizzy or sleepy.
• Headache.
• Feeling nervous and excitable.
• Trouble sleeping.
• Constipation.
• Upset stomach or throwing up.
• Change in taste.

These are not all of the side effects that may occur. If you have questions about side effects, call your doctor. Call your doctor for medical advice about side effects.

You may report side effects to your national health agency.

You may report side effects to the FDA at 1-800-332-1088. You may also report side effects at https://www.fda.gov/medwatch.

How is this drug best taken?

Use this drug as ordered by your doctor. Read all information given to you. Follow all instructions closely.

All oral products:

• Take this drug at the same time of day.
• Keep taking this drug as you have been told by your doctor or other health care provider, even if you feel well.
• Do not take antacids at the same time as this drug. Ask your doctor if you have a question about how to take antacids with this drug.
• If this drug is given through a feeding tube, stop tube feeding for 2 hours before giving this drug. Restart tube feeding 2 hours after giving.

Extended-release capsules:

• Swallow whole. Do not chew, break, or crush.
• Do not take if product changes color.

Chewable tablets:

• Chew or swallow tablet whole.

Suspension:

• Shake well before use.
• Measure liquid doses carefully. Use the measuring device that comes with this drug. If there is none, ask the pharmacist for a device to measure this drug.
• Do not use a household teaspoon or tablespoon to measure this drug. Doing so could lead to the dose being too high.

Injection:

• It is given into a vein for a period of time.

What do I do if I miss a dose?

All oral products:

• Take a missed dose as soon as you think about it.
• If it is close to the time for your next dose, skip the missed dose and go back to your normal time.
• Do not take 2 doses at the same time or extra doses.

Injection:

• Call your doctor to find out what to do.

How do I store and/or throw out this drug?

All oral products:

• Store at room temperature protected from light. Store in a dry place. Do not store in a bathroom.

Suspension:

• Do not freeze.

Injection:

• If you need to store this drug at home, talk with your doctor, nurse, or pharmacist about how to store it.

All products:

• Keep all drugs in a safe place. Keep all drugs out of the reach of children and pets.
• Throw away unused or expired drugs. Do not flush down a toilet or pour down a drain unless you are told to do so. Check with your pharmacist if you have questions about the best way to throw out drugs. There may be drug take-back programs in your area.

General drug facts

• If your symptoms or health problems do not get better or if they become worse, call your doctor.
• Do not share your drugs with others and do not take anyone else’s drugs.
• Some drugs may have another patient information leaflet. If you have any questions about this drug, please talk with your doctor, nurse, pharmacist, or other health care provider.
• This drug comes with an extra patient fact sheet called a Medication Guide. Read it with care. Read it again each time this drug is refilled. If you have any questions about this drug, please talk with the doctor, pharmacist, or other health care provider.
• If you think there has been an overdose, call your poison control center or get medical care right away. Be ready to tell or show what was taken, how much, and when it happened.

Consumer Information Use and Disclaimer

This generalized information is a limited summary of diagnosis, treatment, and/or medication information. It is not meant to be comprehensive and should be used as a tool to help the user understand and/or assess potential diagnostic and treatment options. It does NOT include all information about conditions, treatments, medications, side effects, or risks that may apply to a specific patient. It is not intended to be medical advice or a substitute for the medical advice, diagnosis, or treatment of a health care provider based on the health care provider’s examination and assessment of a patient’s specific and unique circumstances. Patients must speak with a health care provider for complete information about their health, medical questions, and treatment options, including any risks or benefits regarding use of medications. This information does not endorse any treatments or medications as safe, effective, or approved for treating a specific patient. UpToDate, Inc. and its affiliates disclaim any warranty or liability relating to this information or the use thereof. The use of this information is governed by the Terms of Use, available at https://www.wolterskluwer.com/en/know/clinical-effectiveness-terms.

Last Reviewed Date

2024-07-12

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