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Fosphenytoin (By injection)

Fosphenytoin (fos-FEN-i-toin)

Treats and prevents seizures.

Brand Name(s):

Cerebyx, Cerebyx Novaplus

There may be other brand names for this medicine.

When This Medicine Should Not Be Used:

This medicine is not right for everyone. You should not receive it if you had an allergic reaction to fosphenytoin or similar medicines, if you are pregnant, if you have certain heart rhythm problems, or if you have had liver problems from using fosphenytoin or phenytoin.

How to Use This Medicine:


  • This medicine is usually given only for a short time when you cannot take other forms of anticonvulsant medicine, such as when you are in the hospital or when you have surgery.
  • A nurse or other trained health professional will give you this medicine in a hospital. This medicine is given as a shot into a muscle or into a vein.
  • After your condition improves, your doctor might switch you to an oral medicine that works the same way. Talk to your doctor if you have any concerns about this.

Drugs and Foods to Avoid:

Ask your doctor or pharmacist before using any other medicine, including over-the-counter medicines, vitamins, and herbal products.

  • Do not use this medicine together with delavirdine.
  • The list below includes some of the medicines that can interact with fosphenytoin. There are many other drugs not listed. Make sure your doctor knows the names of all the medicines you use, especially the following:
    • Amiodarone, aspirin, chlordiazepoxide, chlorpropamide, cimetidine, clozapine, cyclosporine, diazepam, diazoxide, digoxin, disulfiram, folic acid, furosemide, isoniazid, methadone, methylphenidate, mexiletine, nifedipine, nimodipine, nisoldipine, omeprazole, quinidine, reserpine, rifampin, St John's wort, theophylline, tolbutamide, verapamil, vitamin D supplements
    • Birth control pills
    • Blood thinner (including ticlopidine, warfarin)
    • Cancer medicine
    • HIV/AIDS medicine
    • Medicine to lower cholesterol
    • Medicine to treat depression
    • Medicine to treat infection (including chloramphenicol, miconazole)
    • Other medicines to treat seizures (including carbamazepine, lamotrigine)
    • Phenothiazine medicine (including chlorpromazine, perphenazine, prochlorperazine, promethazine, thioridazine)
    • Steroid medicine (including dexamethasone, hydrocortisone, methylprednisolone, prednisolone, prednisone)
  • Do not drink alcohol while you are using this medicine.

Warnings While Using This Medicine:

  • It is not safe to take this medicine during pregnancy. It could harm an unborn baby. Tell your doctor right away if you become pregnant.
  • Tell your doctor if you are breastfeeding, or if you have kidney disease, liver disease, heart failure, low blood pressure, or porphyria.
  • This medicine may cause the following problems:
    • Serious skin reactions (may happen after treatment has stopped)
    • Drug reaction with eosinophilia and systemic symptoms (DRESS), which may damage organs such as the liver, kidney, or heart
    • Liver problems
    • Higher blood sugar levels
  • This medicine may make you dizzy or drowsy. Do not drive or do anything that could be dangerous until you know how this medicine affects you.
  • Do not stop using this medicine suddenly. Your doctor will need to slowly decrease your dose before you stop it completely.
  • Tell any doctor or dentist who treats you that you are using this medicine. This medicine may affect certain medical test results.
  • Your doctor will do lab tests at regular visits to check on the effects of this medicine. Keep all appointments.

Possible Side Effects While Using This Medicine:

Call your doctor right away if you notice any of these side effects:

  • Allergic reaction: Itching or hives, swelling in your face or hands, swelling or tingling in your mouth or throat, chest tightness, trouble breathing
  • Blistering, peeling, red skin rash
  • Dark urine or pale stools, nausea, vomiting, loss of appetite, stomach pain, yellow skin or eyes
  • Fast, slow, or pounding heartbeat, lightheadedness or fainting
  • Fever, chills, cough, sore throat, and body aches
  • Fever, skin rash, or swollen glands in your armpits, neck, or groin
  • Pain, changes in skin color, or swelling at or near the injection site
  • Severe confusion, problems with balance or walking, slurred speech, tremors
  • Unusual bleeding, bruising, or weakness

If you notice these less serious side effects, talk with your doctor:

  • Burning, itching, or tingling feeling
  • Mild confusion, slurred speech, clumsiness, problems with balance

If you notice other side effects that you think are caused by this medicine, tell your doctor

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088

Last Updated: 5/1/2020

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites.

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