Generic Name: fosphenytoin (fos FEN i toyn)
Brand Name: Cerebyx
Medically reviewed on December 5, 2017.
What is fosphenytoin?
Fosphenytoin is an anticonvulsant that works by slowing down impulses in the brain that cause seizures.
Fosphenytoin is used to prevent or control seizures. Fosphenytoin is used only for a short time when other forms of phenytoin cannot be given.
Fosphenytoin may also be used for purposes not listed in this medication guide.
You should not use fosphenytoin if you also take delavirdine (Rescriptor), or if you have certain serious heart conditions such as slow heartbeats, heart block, AV block, or Adams-Stokes syndrome (a heart rhythm disorder).
Before taking this medicine
You should not use fosphenytoin if you also take delavirdine (Rescriptor), if you are allergic to fosphenytoin or phenytoin (Dilantin), or if you have certain serious heart conditions such as:
heart block, AV block; or
Adams-Stokes syndrome (a heart rhythm disorder).
To make sure fosphenytoin is safe for you, tell your doctor if you have ever had:
porphyria (a genetic enzyme disorder that causes symptoms affecting the skin or nervous system);
if you drink large amounts of alcohol.
Patients of Asian ancestry may have a higher risk of developing a rare but serious skin reaction to fosphenytoin. Your doctor may recommend a blood test before you start the medication to determine your risk of this skin reaction.
Tell your doctor if you are pregnant. Fosphenytoin may cause harm to an unborn baby, but having a seizure during pregnancy could harm both mother and baby. The benefit of preventing seizures may outweigh any risks to the baby.
If you have received fosphenytoin during pregnancy, be sure to tell the doctor who delivers your baby about your fosphenytoin use. Both you and the baby may need to receive medications to prevent excessive bleeding during delivery and just after birth.
Fosphenytoin can pass into breast milk, but effects on the nursing baby are not known. Tell your doctor if you are breast-feeding.
How is fosphenytoin given?
Follow all directions on your prescription label. Do not use this medicine in larger or smaller amounts or for longer than recommended.
Fosphenytoin is injected into a muscle, or into a vein through an IV. You may be shown how to use an IV at home. Do not give yourself this medicine if you do not understand how to use the injection and properly dispose of needles, IV tubing, and other items used.
Your breathing, blood pressure, oxygen levels, kidney function, and other vital signs will be watched closely while you are receiving fosphenytoin in a clinic or hospital setting. Your heart function may also need to be checked using an electrocardiograph or ECG (sometimes called an EKG). You will be watched closely for 10 or 20 minutes after receiving fosphenytoin, to be sure this medication is not causing harmful effects.
Do not stop using fosphenytoin or your other seizure medications suddenly, even if you feel fine. Stopping suddenly may cause increased seizures. Follow your doctor's instructions about tapering your dose.
This medication can cause unusual results with certain medical tests. Tell any doctor who treats you that you are using fosphenytoin.
Store fosphenytoin in the refrigerator, do not freeze.
You may also store this medicine at room temperature, but only for up to 48 hours.
Do not use fosphenytoin if it has changed colors or has particles in it. Call your pharmacist for new medication.
Use a disposable needle and syringe only once. Follow any state or local laws about throwing away used needles and syringes. Use a puncture-proof "sharps" disposal container (ask your pharmacist where to get one and how to throw it away). Keep this container out of the reach of children and pets.
What happens if I miss a dose?
Call your doctor for instructions if you miss a dose of fosphenytoin.
What happens if I overdose?
Seek emergency medical attention or call the Poison Help line at 1-800-222-1222. An overdose of fosphenytoin can be fatal.
What should I avoid while using fosphenytoin?
Avoid drinking alcohol while you are receiving fosphenytoin. Alcohol use can increase your blood levels of fosphenytoin and may increase side effects. Daily alcohol use can decrease your blood levels of fosphenytoin, which can increase your risk of seizures.
Fosphenytoin side effects
Get emergency medical help if you have signs of an allergic reaction (hives, difficult breathing, swelling in your face or throat) or a severe skin reaction (fever, sore throat, burning in your eyes, skin pain, red or purple skin rash that spreads and causes blistering and peeling).
Seek medical treatment if you have a serious drug reaction that can affect many parts of your body. Symptoms may include: skin rash, fever, swollen glands, flu-like symptoms, muscle aches, severe weakness, unusual bruising, or yellowing of your skin or eyes. This reaction may occur several weeks after you began using fosphenytoin.
Call your doctor at once if you have:
very slow heartbeats, shortness of breath;
a light-headed feeling, like you might pass out;
confusion, unusual thoughts or behavior;
a tingling or burning sensation;
easy bruising, unusual bleeding;
purple discoloration of your skin around the IV needle;
sudden weakness or ill feeling, fever, chills, sore throat, mouth sores, red or swollen gums, trouble swallowing; o
Common side effects may include:
unusual or involuntary eye movements;
problems with balance or muscle movement.
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
See also: Side effects (in more detail)
What other drugs will affect fosphenytoin?
Sometimes it is not safe to use certain medications at the same time. Some drugs can raise or lower your blood levels of fosphenytoin, which may cause side effects or make fosphenytoin less effective. Fosphenytoin can also affect blood levels of certain other drugs, making them less effective or increasing side effects.
Taking this medicine with other drugs that make you sleepy can worsen this effect. Ask your doctor before taking fosphenytoin with a sleeping pill, narcotic pain medicine, muscle relaxer, or medicine for anxiety, depression, or seizures.
Many drugs can interact with fosphenytoin. Not all possible interactions are listed here. TELL YOUR DOCTOR ABOUT ALL OTHER MEDICINES YOU USE, and any you start or stop using during treatment with fosphenytoin. This includes prescription and over-the-counter medicines, vitamins, and herbal products.
Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.
Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.
Copyright 1996-2018 Cerner Multum, Inc. Version: 4.01.
More about fosphenytoin
- Fosphenytoin Side Effects
- During Pregnancy
- Dosage Information
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- Drug class: hydantoin anticonvulsants
Other brands: Cerebyx