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Medications and Drugs

Brand Names: Cerebyx

Generic Name: fosphenytoin (Pronunciation: fos FEN i toyn)

What is fosphenytoin (Cerebyx)?

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 are the possible side effects of fosphenytoin (Cerebyx)?

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.

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 is the most important information I should know about fosphenytoin (Cerebyx)?

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).

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.

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.

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.

Report Problems to the Food and Drug Administration

You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.

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