fosphenytoin

Pronunciation: fos FEN i toyn

Brand: Cerebyx

What is the most important information I should know about fosphenytoin?

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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).

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.

What should I discuss with my healthcare provider before I receive fosphenytoin?

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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:

  • slow heartbeats;
  • 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:

  • heart disease;
  • kidney disease;
  • liver disease;
  • low blood pressure;
  • porphyria (a genetic enzyme disorder that causes symptoms affecting the skin or nervous system);
  • diabetes; or
  • 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.

FDA pregnancy category D. Fosphenytoin may cause harm to an unborn baby, but having a seizure during pregnancy could harm both the mother and the baby. Tell your doctor if you are pregnant.

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Fosphenytoin can make birth control pills less effective. Ask your doctor about using non hormonal birth control (condom, diaphragm with spermicide) to prevent pregnancy while you are receiving fosphenytoin.

Seizure control is very important during pregnancy. The benefit of preventing seizures may outweigh any risks posed by using fosphenytoin. Follow your doctor's instructions about receiving fosphenytoin if you are pregnant.

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.

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It is not known whether fosphenytoin passes into breast milk or if it could harm a nursing baby. You should not breast-feed while you are using fosphenytoin.

How is fosphenytoin given?

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 self-inject this medicine if you do not understand how to give the injection and properly dispose of used needles, IV tubing, and other items used to inject the medicine.

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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.

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.

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.

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Store fosphenytoin in the refrigerator, do not freeze.

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You may also store this medicine at room temperature, but only for 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.

What happens if I miss a dose?

Call your doctor for instructions if you miss a dose of fosphenytoin.

What happens if I overdose?

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Seek emergency medical attention or call the Poison Help line at 1-800-222-1222. An overdose of fosphenytoin can be fatal.

Overdose symptoms may include weakness, nausea, vomiting, feeling light-headed, chest pain, fast or slow heart rate, weak pulse, slow breathing (breathing may stop).

What should I avoid while using fosphenytoin?

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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.

What are the possible side effects of fosphenytoin?

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Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

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Call your doctor at once if you have:

  • irregular heart rhythm, feeling short of breath;
  • a light-headed feeling, like you might pass out;
  • sudden weakness or ill feeling, fever, chills, sore throat, mouth sores, red or swollen gums, trouble swallowing;
  • liver problems --nausea, upper stomach pain, itching, tired feeling, loss of appetite, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes);
  • low potassium --confusion, uneven heart rate, extreme thirst, increased urination, leg discomfort, muscle weakness or limp feeling;
  • signs of inflammation in your body --swollen glands, flu symptoms, easy bruising or bleeding, severe tingling or numbness, muscle weakness, chest pain, new or worsening cough with fever; or
  • severe skin reaction --fever, sore throat, swelling in your face or tongue, burning in your eyes, skin pain, followed by a red or purple skin rash that spreads (especially in the face or upper body) and causes blistering and peeling.

Common side effects may include:

  • headache, dizziness;
  • drowsiness;
  • back-and-forth movements of the eyes;
  • itching; or
  • numbness or tingling.

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.

What other drugs will affect fosphenytoin?

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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.

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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.

Where can I get more information?

Your pharmacist can provide more information about fosphenytoin.


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.

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