Fosphenytoin

Generic Name: fosphenytoin (FOS-fen-i-toyn)
Brand Name: Cerebyx

Severe low blood pressure and irregular heartbeat have been reported in patients taking fosphenytoin. The risk may be increased if it is given faster than recommended. Contact your doctor right away if you develop an irregular heartbeat or symptoms of low blood pressure (eg, fainting, severe or persistent dizziness or light-headedness).


Fosphenytoin is used for:

Treating certain types of severe seizures (eg, status epilepticus). It is also used to prevent and treat seizures that may occur during or after brain or nervous system surgery. It may also be used for other conditions as determined by your doctor.

Fosphenytoin is an anticonvulsant. It works in the brain to block the spread of seizure activity.

Do NOT use fosphenytoin if:

  • you are allergic to any ingredient in fosphenytoin or to other hydantoins (eg, phenytoin)
  • you have certain types of heart problems (eg, very slow heartbeat, certain types of heart block, Adams-Stokes syndrome)
  • you are taking apixaban, axitinib, bortezomib, cabazitaxel, crizotinib, delavirdine, dronedarone, etravirine, ivacaftor, lurasidone, mifepristone, nifedipine, nisoldipine, praziquantel, ranolazine, rilpivirine, rivaroxaban, roflumilast, ticagrelor, or vandetanib

Contact your doctor or health care provider right away if any of these apply to you.

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Before using fosphenytoin:

Some medical conditions may interact with fosphenytoin. Tell your doctor or pharmacist if you have any medical conditions, especially if any of the following apply to you:

  • if you are pregnant, planning to become pregnant, or are breast-feeding
  • if you are taking any prescription or nonprescription medicine, herbal preparation, or dietary supplement
  • if you have allergies to medicines, foods, or other substances
  • if you or a family member have had an allergic reaction to a barbiturate (eg, phenobarbital), carbamazepine, an oxazolidinedione (eg, trimethadione), oxcarbazepine, or a succinimide (eg, ethosuximide, methsuximide)
  • if you have heart problems (eg, heart block), low blood pressure, the blood disease porphyria, liver or kidney disease, low blood albumin levels, diabetes, bone marrow problems, or a history of lymph gland problems
  • if you are in very poor health
  • if you drink alcohol or have a history of alcohol abuse
  • if you have been tested and know whether or not you have a gene type called HLA-B*1502
  • if you have a history of mental or mood problems (eg, depression), or suicidal thoughts or attempts

Some MEDICINES MAY INTERACT with fosphenytoin. Tell your health care provider if you are taking any other medicines, especially any of the following:

  • Many other prescription and nonprescription medicines (eg, used for allergic reactions, asthma or other breathing problems, blood thinning, diabetes, infections, inflammation, aches and pains, attention deficit hyperactivity disorder, alcoholism, cancer, erectile dysfunction, high blood pressure, indigestion, irregular heartbeat or other heart problems, hepatitis C, high blood iron levels, high cholesterol, HIV, birth control, hormone replacement, immune system suppression, low blood sugar, mental or mood problems, narcotic addiction, pain, seizures, stomach or bowel problems, trouble sleeping), multivitamin products, and herbal or dietary supplements (eg, herbal teas, coenzyme Q10, garlic, ginseng, ginkgo, St. John's wort) may interact with fosphenytoin. Ask your doctor or pharmacist if you are unsure if any of your medicines might interact with fosphenytoin

This may not be a complete list of all interactions that may occur. Ask your health care provider if fosphenytoin may interact with other medicines that you take. Check with your health care provider before you start, stop, or change the dose of any medicine.

How to use fosphenytoin:

Use fosphenytoin as directed by your doctor. Check the label on the medicine for exact dosing instructions.

  • Fosphenytoin is usually given as an injection at your doctor's office, hospital, or clinic. If you will be using fosphenytoin at home, a health care provider will teach you how to use it. Be sure you understand how to use fosphenytoin. Follow the procedures you are taught when you use a dose. Contact your health care provider if you have any questions.
  • Do not use fosphenytoin if it contains particles, is cloudy or discolored, or if the vial is cracked or damaged.
  • Do not suddenly stop taking fosphenytoin. You may have an increased risk of seizures. If you need to stop fosphenytoin, your doctor will gradually lower your dose.
  • Keep this product, as well as syringes and needles, out of the reach of children and pets. Do not reuse needles, syringes, or other materials. Ask your health care provider how to dispose of these materials after use. Follow all local rules for disposal.
  • If you miss a dose of fosphenytoin, contact your doctor right away.

Ask your health care provider any questions you may have about how to use fosphenytoin.

Important safety information:

  • Fosphenytoin may cause dizziness or drowsiness. These effects may be worse if you take it with alcohol or certain medicines. Use fosphenytoin with caution. Do not drive or perform other possibly unsafe tasks until you know how you react to it.
  • Check with your doctor before you drink alcohol while you are taking fosphenytoin. Alcohol may increase or decrease the amount of medicine in your blood.
  • Do NOT take more than the recommended dose or use for longer than prescribed without checking with your doctor.
  • Patients who take fosphenytoin may be at increased risk for suicidal thoughts or actions. The risk may be greater in patients who have had suicidal thoughts or actions in the past. Watch patients who take fosphenytoin closely. Contact the doctor at once if new, worsened, or sudden symptoms such as depressed mood; anxious, restless, or irritable behavior; panic attacks; or any unusual change in mood or behavior occur. Contact the doctor right away if any signs of suicidal thoughts or actions occur.
  • Proper dental care is important while you are taking fosphenytoin. Brush and floss your teeth and visit the dentist regularly.
  • Fosphenytoin may raise your blood sugar. High blood sugar may make you feel confused, drowsy, or thirsty. It can also make you flush, breathe faster, or have a fruit-like breath odor. If these symptoms occur, tell your doctor right away.
  • There have been reports of lymph node problems, including cancer, in patients who take fosphenytoin. It is not known if fosphenytoin may be the cause. Contact your doctor right away if you develop swollen lymph nodes.
  • A serious and sometimes fatal reaction has been reported in patients taking medicines for seizures, including fosphenytoin. Contact your doctor right away if you develop swollen lymph nodes, fever, rash, chest pain, symptoms of kidney problems (eg, decreased urination), or symptoms of liver problems (eg, dark urine, loss of appetite, pale stools, stomach pain, yellowing of the skin or eyes).
  • Tell your doctor or dentist that you take fosphenytoin before you receive any medical or dental care, emergency care, or surgery.
  • Hormonal birth control (eg, birth control pills) may not work as well while you are using fosphenytoin. To prevent pregnancy, use an extra form of birth control (eg, condoms).
  • Serious and sometimes fatal skin reactions have been reported with fosphenytoin. Patients who have a certain gene type called HLA-B*1502 may have an increased risk for these skin reactions. This gene type is found most commonly in Asian patients. Tell your doctor if you have been tested and know whether or not you have the HLA-B*1502 gene type. Discuss any questions or concerns with your doctor.
  • Fosphenytoin may interfere with certain lab tests. Be sure your doctor and lab personnel know you are taking fosphenytoin.
  • Lab tests, including blood phenytoin levels or liver function tests, may be performed while you use fosphenytoin. These tests may be used to monitor your condition or check for side effects. Be sure to keep all doctor and lab appointments.
  • Use fosphenytoin with caution in the ELDERLY; they may be more sensitive to its effects.
  • Fosphenytoin should be used with extreme caution in CHILDREN; safety and effectiveness in children have not been confirmed.
  • Women who take fosphenytoin may experience an increase in seizure activity if they become pregnant. Discuss any questions or concerns with your doctor. If you think you may be pregnant, contact your doctor.
  • Fosphenytoin may cause harm to the fetus. If you may become pregnant, discuss other possible treatment options with your doctor. If a decision is made to take fosphenytoin, use effective birth control while you are taking it. Talk with your doctor if you are planning to become pregnant, or if you have questions or concerns about this information.
  • PREGNANCY and BREAST-FEEDING: Fosphenytoin may cause harm to the fetus. If you think you may be pregnant, contact your doctor right away. You will need to discuss the benefits and risks of using fosphenytoin while you are pregnant. You and your doctor will need to decide if you will continue to take fosphenytoin while you are pregnant. It is not known if fosphenytoin is found in breast milk. Do not breast-feed while taking fosphenytoin.

Possible side effects of fosphenytoin:

All medicines may cause side effects, but many people have no, or minor, side effects. Check with your doctor if any of these most COMMON side effects persist or become bothersome:

Dizziness; drowsiness; dry mouth; headache; nausea; pelvic pain; vomiting.

Seek medical attention right away if any of these SEVERE side effects occur:

Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue); bone pain; burning, numbness, or tingling; butterfly-shaped rash on the face; chest pain; clumsiness or unsteadiness; confusion; decreased coordination; delirium; fast, slow, or irregular heartbeat; hearing problems (eg, ringing in the ears, hearing loss); new or worsening mental or mood changes (eg, agitation, anxiety, behavior changes, depression, irritability, panic attacks, restlessness, suicidal thoughts or attempts); new or worsening seizures; muscle pain, weakness, or cramping; pain, swelling, or redness at or near the injection site; red, swollen, blistered, or peeling skin; severe or persistent dizziness, light-headedness, headache, or drowsiness; severe or persistent trouble sleeping; signs of infection (eg, fever, chills, sore throat); sluggishness; sores in the mouth or around the eyes; speech problems; swollen lymph nodes; swollen or tender gums; symptoms of liver problems (eg, dark urine, loss of appetite, pale stools, stomach pain, yellowing of the skin or eyes); tremor; unusual bruising or bleeding; unusual eye movements; unusual muscle movements; unusual tiredness or weakness; vision changes.

This is not a complete list of all side effects that may occur. If you have questions about side effects, contact your health care provider. Call your doctor for medical advice about side effects. To report side effects to the appropriate agency, please read the Guide to Reporting Problems to FDA.

If OVERDOSE is suspected:

Contact 1-800-222-1222 (the American Association of Poison Control Centers), your local poison control center, or emergency room immediately. Symptoms may include confusion; decreased coordination; fainting; fast, slow, or irregular heartbeat; loss of consciousness; severe dizziness or drowsiness; severe or persistent nausea or vomiting; slow or difficult breathing; sluggishness; speech problems (eg, slurred speech); symptoms of low blood calcium levels (eg, muscle aches, cramps, or spasms; numbness or tingling of the lips, tongue, fingers, or feet; seizures); tremor; unusual eye movements.

Proper storage of fosphenytoin:

Fosphenytoin is usually handled and stored by a health care provider. If you are using fosphenytoin at home, store fosphenytoin as directed by your pharmacist or health care provider. Keep fosphenytoin out of the reach of children and away from pets.

General information:

  • If you have any questions about fosphenytoin, please talk with your doctor, pharmacist, or other health care provider.
  • Fosphenytoin is to be used only by the patient for whom it is prescribed. Do not share it with other people.
  • If your symptoms do not improve or if they become worse, check with your doctor.
  • Check with your pharmacist about how to dispose of unused medicine.

This information should not be used to decide whether or not to take fosphenytoin or any other medicine. Only your health care provider has the knowledge and training to decide which medicines are right for you. This information does not endorse any medicine as safe, effective, or approved for treating any patient or health condition. This is only a brief summary of general information about fosphenytoin. It does NOT include all information about the possible uses, directions, warnings, precautions, interactions, adverse effects, or risks that may apply to fosphenytoin. This information is not specific medical advice and does not replace information you receive from your health care provider. You must talk with your healthcare provider for complete information about the risks and benefits of using fosphenytoin.

Issue Date: July 2, 2014
Database Edition 14.3.1.001
Copyright © 2014 Wolters Kluwer Health, Inc.

Disclaimer: This information should not be used to decide whether or not to take this medicine or any other medicine. Only your health care provider has the knowledge and training to decide which medicines are right for you. This information does not endorse any medicine as safe, effective, or approved for treating any patient or health condition. This is only a brief summary of general information about this medicine. It does NOT include all information about the possible uses, directions, warnings, precautions, interactions, adverse effects, or risks that may apply to this medicine. This information is not specific medical advice and does not replace information you receive from your health care provider. You must talk with your healthcare provider for complete information about the risks and benefits of using this medicine.

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