Phenytoin (Injection)


Phenytoin (FEN-i-toin)

Treats certain types of seizures (epilepsy). This medicine is an anticonvulsant.

Brand Name(s)

There may be other brand names for this medicine.

When This Medicine Should Not Be Used

You should not receive this medicine if you have had an allergic reaction to phenytoin or to similar medicines (such as ethotoin, fosphenytoin, or Cerebyx®). Do not receive this medicine if you are pregnant or if you also use delavirdine (Rescriptor®). Do not receive this medicine if you have certain heart rhythm problems.

How to Use This Medicine


  • Your doctor will prescribe your exact dose and tell you how often it should be given. This medicine is given through a needle placed in one of your veins. It may also be given as a shot into one of your muscles.
  • A nurse or other trained health professional will give you this medicine.
  • Your doctor will give you a few doses of this medicine until your condition improves. Then you will be switched 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.

  • Make sure your doctor knows if you also use amiodarone (Cordarone®), aspirin, chloramphenicol (Chloromycetin®, Chloroptic®), chlordiazepoxide (Librium®), diazepam (Valium®), disulfiram (Antabuse®), fluorouracil, halothane (Fluothane®), isoniazid (Nydrazid®), methylphenidate (Ritalin®), sucralfate (Carafate®), or tolbutamide (Orinase®). Tell your doctor if you use other medicines to treat seizures (such as carbamazepine, ethosuximide, felbamate, oxcarbazepine, phenobarbital, quetiapine, sodium valproate, topiramate, trimethadione, valproic acid, Klonopin®, Tegretol®, Topamax®, or Zarontin®), medicine to treat fungal infections (such as fluconazole, itraconazole, ketoconazole, voriconazole, Nizoral®, Sporanox®, or Vfend®), medicine to treat depression (such as fluoxetine, fluvoxamine, paroxetine, sertraline, trazodone, Paxil®, or Prozac®), stomach medicines (such as cimetidine, omeprazole, ranitidine, Prilosec®, Tagamet®, or Zantac®), a phenothiazine medicine (such as prochlorperazine, Compazine®, Mellaril®, Phenergan®, Thorazine®, or Trilafon®), or a blood thinner (such as warfarin, Coumadin®).
  • Tell your doctor if you also use doxycycline (Vibramycin®), furosemide (Lasix®), irinotecan (Camptosar®), paclitaxel (Taxol®), quinidine (Cardioquin®), reserpine, rifampin (Rifadin®, Rimactane®), teniposide (Vumon®), theophylline (Theo-Dur®), Vitamin D, medicine to treat HIV infection (such as amprenavir, efavirenz, indinavir, lopinavir, nelfinavir, ritonavir, saquinavir, Fortovase®, Invirase®, Kaletra®, or Sustiva®), steroid medicine (such as dexamethasone, prednisolone, prednisone, or Medrol®), or birth control pills.
  • Do not drink alcohol while you are using this medicine.

Warnings While Using This Medicine

  • Using this medicine while you are pregnant can harm your unborn baby. Use an effective form of birth control to keep from getting pregnant. If you think you have become pregnant while using the medicine, tell your doctor right away.
  • Make sure your doctor knows if you are breastfeeding or if you have kidney disease, liver disease, blood or bone marrow problems, bone problems (such as osteoporosis), heart failure, low blood pressure, lymph node problem (such as lymphadenopathy), an enzyme problem (such as porphyria), or diabetes.
  • Do not stop using this medicine suddenly without asking your doctor. You may need to slowly decrease your dose before stopping it completely.Your seizures may return or occur more often if you stop this medicine suddenly.
  • Tell your doctor right away if you develop a fever; rash; swollen, painful, or tender glands in the neck, armpit, or groin; unusual bleeding or bruising; or yellow eyes or skin. These may be symptoms of a serious and life-threatening reaction to this medicine.
  • This medicine may make you dizzy or drowsy. Do not drive, use machines, or do anything else that could be dangerous until you know how this medicine affects you.
  • This medicine may raise or lower your blood sugar, or it may cover up symptoms of very low blood sugar (hypoglycemia).
  • Be sure to talk to your doctor if you develop any unusual or strange thoughts and behavior while you receive phenytoin injection. Some changes that have occurred in people who receive this medicine are like those seen in people who drink too much alcohol. Other changes might be confusion, worsening of depression, hallucinations, suicidal thoughts, and unusual excitement, nervousness, or irritability.
  • Make sure any doctor or dentist who treats you knows that you are using this medicine. This medicine may affect the results of certain medical tests.
  • This medicine lowers the number of some types of blood cells in your body. Because of this, you may bleed or get infections more easily. To help with these problems, avoid being near people who are sick or have infections. Wash your hands often. Stay away from rough sports or other situations where you could be bruised, cut, or injured. Brush and floss your teeth gently. Be careful when using sharp objects, including razors and fingernail clippers.
  • Birth control pills may not work while you are using this medicine. Use another form of birth control along with your birth control pills to avoid pregnancy.
  • Your doctor will need to check your progress at regular visits while you are using this medicine. Be sure to keep all appointments. Blood tests may also be needed to check for side effects.

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, or red skin rash
  • Dark-colored urine or pale stools
  • Fast, slow, or uneven heartbeats
  • Fever, chills, cough, sore throat, and body aches
  • Lightheadedness, dizziness, or fainting
  • Loss of seizure control
  • Nausea, vomiting, loss of appetite, or pain in your upper stomach
  • Numbness, tingling, or burning pain in your arms, legs, or feet
  • Pain, changes in skin color, or swelling at or near the injection site
  • Severe confusion, trembling, problems with speech, or problems with muscle control or coordination
  • Tender glands in the neck, armpit, or groin
  • Uncontrolled eye movements
  • Unusual bleeding, bruising, tiredness, or weakness
  • Yellowing of your skin or the whites of your eyes

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

  • Confusion, nervousness, or trouble sleeping
  • Mild skin rash

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

Version Info

  • Last Reviewed on 06/12/2013

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This page was last updated: June 18, 2013

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