Fosphenytoin

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

Cerebyx

Brand Names: Canada

Cerebyx

What is this drug used for?

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

What do I need to tell the doctor BEFORE my child takes this drug?

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

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 the doctor and pharmacist about all of your child’s drugs (prescription or OTC, natural products, vitamins) and health problems. You must check to make sure that it is safe to give this drug with all of your child’s other drugs and health problems. Do not start, stop, or change the dose of any drug your child takes without checking with the doctor.

What are some things I need to know or do while my child takes this drug?

• Tell all of your child’s health care providers that your child is taking this drug. This includes your child’s doctors, nurses, pharmacists, and dentists.
• Have your child wear disease medical alert ID (identification).
• Have your child avoid tasks or actions that call for alertness until you see how this drug affects your child. These are things like riding a bike, playing sports, or using items such as scissors, lawnmowers, electric scooters, toy cars, or motorized vehicles.
• If your child is old enough to drive, have your child follow laws about driving with a seizure problem.
• If seizures are different or worse after starting this drug, talk with the doctor.
• Do not stop giving this drug to your child all of a sudden without calling the doctor. Your child may have a greater risk of seizures. If your child needs to stop this drug, you will want to slowly stop it as told by the doctor.
• Have blood work checked as you have been told by the doctor. Talk with the doctor.
• Have the level of phenytoin in your child’s blood checked as you have been told by the 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 the doctor.
• If your child has high blood sugar (diabetes), you will need to watch your child’s blood sugar closely.
• Alcohol may interact with this drug. Be sure your child does not drink alcohol.
• Talk with your child’s doctor before your child uses marijuana, other forms of cannabis, or prescription or OTC drugs that may slow your child’s actions.
• This drug may affect certain lab tests. Tell all of your child’s health care providers and lab workers that your child takes this drug.
• 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.

If your child is or may be sexually active:

• Birth control pills and other hormone-based birth control may not work as well to prevent pregnancy. Be sure your child uses some other kind of birth control also, like a condom, when taking this drug.

If your child is pregnant:

• This drug may cause harm to the unborn baby if your child takes it during pregnancy. If your child is pregnant or gets pregnant while taking this drug, call the doctor right away.
• A bleeding problem that can be life-threatening may happen in newborns if your child took this drug during pregnancy.

If your child is breast-feeding a baby:

• Tell the doctor if your child is breast-feeding a baby. You will need to talk about any risks to the baby.

What are some side effects that I need to call my child’s 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 child’s doctor or get medical help right away if your child has any of the following signs or symptoms that may be related to a very bad side effect:

• 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.
• Very bad dizziness or passing out.
• Trouble controlling body movements, twitching, change in balance, trouble swallowing or speaking.
• Feeling confused.
• Ringing in ears.
• Hearing loss.
• Shakiness.
• Not able to control eye movements.
• Swelling, pain, or change in skin color near the injection site or down the arm/hand.
• A burning, numbness, or tingling feeling that is not normal.
• A severe skin reaction (Stevens-Johnson syndrome/toxic epidermal necrolysis) may happen. It can cause severe health problems that may not go away, and sometimes death. Get medical help right away if your child has signs like red, swollen, blistered, or peeling skin (with or without fever); red or irritated eyes; or sores in the mouth, throat, nose, or eyes.
• A severe and sometimes deadly effect has happened in people taking drugs for seizures like this drug. Call the doctor right away if your child has swollen glands; fever; rash; painful sores in the mouth or around the eyes; chest pain; signs of kidney problems like not able to pass urine or change in how much urine is 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.
• Lymph node problems like cancer have happened in people taking this drug. It is not known if this drug may be the cause. Talk with the doctor if your child has swollen glands.
• Rarely, certain blood problems have happened with this drug. This can lead to bleeding problems or infections. Sometimes, these have been deadly. Tell the doctor right away if your child has 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 the doctor right away if your child has any unexplained bruising or bleeding, pale skin, or feels very tired or weak.

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 child’s doctor or get medical help if any of these side effects or any other side effects bother your child or do not go away:

• Feeling dizzy, sleepy, tired, or weak.
• Headache.
• Upset stomach or throwing up.
• Feeling nervous and excitable.

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

You may report side effects to your national health agency.

How is this drug best given?

Give this drug as ordered by your child’s doctor. Read all information given to you. Follow all instructions closely.

• It is given as a shot into a muscle or as an infusion into a vein over a period of time.

What do I do if my child misses a dose?

• Call your child’s doctor to find out what to do.

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

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

General drug facts

• If your child’s symptoms or health problems do not get better or if they become worse, call your child’s doctor.
• Do not share your child’s drug with others and do not give anyone else’s drug to your child.
• 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.
• Some drugs may have another patient information leaflet. If you have any questions about this drug, please talk with your child’s doctor, nurse, 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

2023-12-26

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