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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 this medication 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).

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Fosphenytoin should not be used together with delavirdine (Rescriptor).

Before receiving fosphenytoin, tell your doctor if you are allergic to any drugs, or if you have heart disease, kidney disease, liver disease, low blood pressure, porphyria, diabetes, or if you drink large amounts of alcohol.

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If possible before you receive fosphenytoin, tell your doctor if you are pregnant. Fosphenytoin may cause harm to an unborn baby, but having a seizure during pregnancy could harm both the mother and the baby. If you become pregnant while using fosphenytoin, DO NOT STOP USING the medicine without your doctor's advice. Seizure control is very important during pregnancy and the benefits of preventing seizures may outweigh any risks posed by using fosphenytoin.

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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There are many other medicines that can interact with fosphenytoin. Tell your doctor about all medications you use. This includes prescription, over-the-counter, vitamin, and herbal products. Do not start a new medication without telling your doctor.

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 this medication 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).

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Fosphenytoin should not be used together with delavirdine (Rescriptor).

To make sure you can safely receive fosphenytoin, tell your doctor if you have any of these other conditions:

  • heart disease;
  • kidney or liver disease;
  • diabetes;
  • low blood pressure;
  • porphyria (a genetic enzyme disorder that causes symptoms affecting the skin or nervous system); 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. If possible before you receive fosphenytoin, tell your doctor if you are pregnant. Fosphenytoin may cause harm to an unborn baby. Use effective birth control to prevent pregnancy while you are using fosphenytoin. Fosphenytoin can make birth control pills less effective. Ask your doctor about using a non hormone method of birth control (such as a condom, diaphragm, spermicide) to prevent pregnancy while receiving fosphenytoin.

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If you become pregnant while using fosphenytoin, DO NOT STOP USING the medicine without your doctor's advice. Although fosphenytoin may harm an unborn baby, having a seizure during pregnancy could harm both mother and baby.

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 using fosphenytoin while 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 injections at home. Do not self-inject this medicine if you do not fully 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 at least 20 minutes after receiving fosphenytoin, to be sure this medication is not causing harmful effects.

Use a disposable needle only once. Throw away used needles in a puncture-proof container (ask your pharmacist where you can get one and how to dispose of it). Keep this container out of the reach of children and pets.

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Do not stop using fosphenytoin without first talking to your doctor, even if you feel fine. You may have increased seizures if you stop using fosphenytoin suddenly without medical advice.

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 in the refrigerator, do not freeze.

Do not use fosphenytoin if it has changed colors or has particles in it. Call your doctor for a new prescription.

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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Tell your caregivers at once if you have a serious side effect such as:

  • severe burning, itching, swelling, redness, or skin discoloration anywhere in the body;
  • problems with vision or speech;
  • feeling like you might pass out;
  • chest pain, irregular heart rhythm, feeling short of breath;
  • fever, swollen glands, body aches, flu symptoms;
  • skin rash, easy bruising or bleeding, severe tingling, numbness, pain, muscle weakness;
  • confusion, nausea and vomiting, swelling, rapid weight gain, urinating less than usual or not at all;
  • new or worsening cough with fever, trouble breathing;
  • upper stomach pain, 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); 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.

Less serious side effects may include:

  • constipation, mild nausea, dry mouth;
  • headache, dizziness, drowsiness;
  • mild itching or tingly feeling;
  • tremor, muscle weakness, loss of coordination;
  • ringing in your ears; or
  • pain in your hips or back.

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?

Drugs that can increase fosphenytoin levels in your blood include:

  • amiodarone (Cordarone, Pacerone);
  • disulfiram (Antabuse);
  • fluorouracil (5FU, Adrucil);
  • ethosuximide (Zarontin);
  • isoniazid (for treating tuberculosis);
  • methylphenidate (Ritalin, Concerta, Daytrana);
  • tolbutamide (Orinase);
  • birth control pills or hormone replacement therapy;
  • chlorpromazine (Thorazine), prochlorperazine (Compazine, Compro), promethazine (Pentazine, Phenergan, Anergan, Antinaus), thioridazine (Mellaril), and other phenothiazines;
  • phenobarbital (Solfoton) or other barbiturates;
  • salicylates such as aspirin, Backache Relief Extra Strength, Novasal, Nuprin Backache Caplet, Doan's Pills Extra Strength, Pepto-Bismol, Tricosal, and others;
  • stomach acid reducers such as cimetidine (Tagamet), ranitidine (Zantac), famotidine (Pepcid), or nizatidine (Axid);
  • certain sedatives (such as Librium, Librax, Limbitrol, or Valium) or antidepressants such as fluoxetine (Prozac, Rapiflux, Sarafem, Selfemra, Symbyax) or trazodone (Desyrel); or
  • sulfa drugs (Bactrim, Septra, Sulfatrim, SMX-TMP, and others).

Drugs that can make fosphenytoin less effective in controlling seizures include:

  • reserpine; or
  • carbamazepine (Carbatrol, Equetro, Tegretol).

Other drugs that can interact with fosphenytoin include:

  • a blood thinner such as warfarin (Coumadin, Jantoven);
  • digoxin (digitalis, Lanoxin);
  • furosemide (Lasix);
  • steroid medications (prednisone and others);
  • theophylline (Elixophyllin, Theo-Dur, Theo-Bid, Theolair, Uniphyl);
  • valproic acid (Depakene) or divalproex sodium (Depakote);
  • an antibiotic such as rifampin (Rimactane, Rifadin, Rifamate) or doxycycline (Doryx, Vibramycin, Adoxa, and others); or
  • an antidepressant such as amitriptyline (Elavil, Vanatrip, Limbitrol), doxepin (Sinequan, Silenor), nortriptyline (Pamelor), and others.
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This list is not complete and there are many other medicines that can interact with fosphenytoin. Tell your doctor about all the prescription and over-the-counter medications you use. This includes vitamins, minerals, herbal products, and drugs prescribed by other doctors. Do not start using a new medication without your doctor's advice.

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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