Phenytoin (By mouth)


Phenytoin (FEN-i-toin)

Treats seizures. This medicine is an anticonvulsant.

Brand Name(s)

Dilantin Kapseals, Dilantin-125, Dilantin Infatabs, Dilantin, Phenytek, Diphen

There may be other brand names for this medicine.

When This Medicine Should Not Be Used

Do not use this medicine if you have had an allergic reaction to phenytoin or similar medicines (such as Cerebyx®, Mesantoin®, or Peganone®) or if you are pregnant. Do not use this medicine if you also use delavirdine (Rescriptor®).

How to Use This Medicine

Capsule, Long Acting Capsule, Liquid, Chewable Tablet

  • Your doctor will tell you how much of this medicine to use and how often. Do not use more medicine or use it more often than your doctor tells you to.
  • You may take this medicine with food if it upsets your stomach. Take this medicine at the same time each day.
  • Swallow the capsule whole. Do not open, crush, or chew it.
  • The chewable tablet may be chewed, swallowed whole, or crushed before swallowing.
  • Shake the oral liquid before each use. Measure the oral liquid medicine with a marked measuring spoon, oral syringe, or medicine cup.
  • If you receive tube feedings, take phenytoin at least 2 hours before or 2 hours after a feeding.
  • This medicine should come with a Medication Guide. Read and follow these instructions carefully. Ask your doctor or pharmacist if you have any questions. Ask your pharmacist for the Medication Guide if you do not have one.

If a dose is missed:

  • If you miss a dose or forget to use your medicine, use it as soon as you can. If it is almost time for your next dose, wait until then to use the medicine and skip the missed dose. Do not use extra medicine to make up for a missed dose.

How to Store and Dispose of This Medicine

  • Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Do not freeze the oral liquid.
  • Ask your pharmacist, doctor, or health caregiver about the best way to dispose of any outdated medicine or medicine no longer needed.
  • Keep all medicine away from children and never share your medicine with anyone.

Drugs and Foods to Avoid

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

  • There are many other drugs that can interact with phenytoin. Make sure your doctor knows about all other medicines you are using.
  • Make sure your doctor knows if you also use amiodarone (Cordarone®), chloramphenicol (Chloromycetin®), chlordiazepoxide (Librium®), diazepam (Valium®), disulfiram (Antabuse®), halothane (Fluothane®), isoniazid (Nydrazid®), methylphenidate (Ritalin®), ticlopidine (Ticlid®), tolbutamide (Orinase®), medicine to treat seizures (such as carbamazepine, ethosuximide, felbamate, methsuximide, oxcarbazepine, phenobarbital, quetiapine, sodium valproate, topiramate, valproic acid, Depakene®, Luminal®, Tegretol®, or Zarontin®), medicine to treat depression (such as amitriptyline, doxepin, fluoxetine, fluvoxamine, nortriptyline, paroxetine, sertraline, trazodone, Desyrel®, Luvox®, Prozac®, or Sinequan®), a stomach medicine (such as cimetidine, omeprazole, ranitidine, Tagamet®, or Zantac®), or a blood thinner (such as dicumarol, warfarin, or Coumadin®).
  • Tell your doctor if you also use aspirin, doxycycline (Vibramycin®), molindone (Moban®), phenylbutazone, reserpine, rifampin (Rifadin®, Rimactane®), sucralfate (Carafate®), theophylline (Theo-Dur®), Vitamin D, medicine for heart problems (such as digitoxin, furosemide, quinidine, or Lasix®), a steroid medicine (such as dexamethasone, prednisolone, prednisone, or Medrol®), or a phenothiazine medicine (such as prochlorperazine, Compazine®, Mellaril®, Phenergan®, Thorazine®, or Trilafon®).
  • Make sure your doctor knows if you also use fluorouracil, irinotecan (Camptosar®), medicines to treat fungal infection (such as fluconazole, itraconazole, ketoconazole, voriconazole, Nizoral®, or Sporanox®), sulfa drugs (such as sulfamethoxazole, sulfasalazine, sulfisoxazole, Azulfidine®, Bactrim®, Gantrisin®, or Septra®), or medicine to treat HIV/AIDS (such as amprenavir, efavirenz, indinavir, lopinavir/ritonavir, nelfinavir, ritonavir, saquinavir, Kaletra®, Norvir®, or Viracept®).
  • If you are using an antacid (Maalox® or Mylanta®), take it least 1 hour after you take phenytoin.
  • Birth control pills may not work while you are using phenytoin. To avoid pregnancy, use another form of birth control.
  • 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, lymph node problems (such as lymphadenopathy), bone problems (such as osteoporosis), diabetes, or porphyria.
  • Do not stop using this medicine suddenly without asking your doctor. You may need to slowly decrease your dose before stopping it completely.
  • This medicine can increase thoughts of suicide. Although this is a risk for all patients, it is more likely in children, teenagers, and young adults. Tell your doctor right away if you feel depressed and have thoughts about hurting yourself. Report any unusual thoughts or behaviors that trouble you, especially if they are new or get worse quickly. Tell your doctor if you or anyone in your family has bipolar disorder (manic-depressive) or has tried to commit suicide.
  • Tell your doctor right away if you develop a fever, rash, swollen or tender glands, unusual bleeding or bruising, or yellow eyes or skin after receiving this medicine. These may be symptoms of a serious and life-threatening reaction to this medicine.
  • This medicine may decrease bone mineral density. A low bone mineral density can cause weak bones or osteoporosis. Talk to your doctor if you have any questions about this.
  • 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.
  • This medicine may affect blood sugar levels. If you notice a change in the results of your blood or urine sugar tests or if you have any questions, check with your doctor.
  • 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 may make you drowsy. Do not drive, use machines, or do anything else that could be dangerous until you know how this medicine affects you.
  • Your doctor will need to check your blood at regular visits while you are using this medicine. Be sure to 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, or red skin rash
  • Confusion, problems with balance or walking, slurred speech, tremors, or uncontrolled eye movements
  • Dark-colored urine or pale stools
  • Feeling depressed, irritable, or restless
  • Fever, chills, cough, sore throat, and body aches
  • Nausea, vomiting, loss of appetite, or pain in your upper stomach
  • Numbness, tingling, or burning pain in your hands, arms, legs, or feet
  • Swollen glands in your armpits, neck, or groin
  • Unusual bleeding, bruising, or weakness
  • Unusual thoughts or behaviors, thoughts of hurting yourself
  • Yellow skin or eyes

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

  • Constipation
  • Dizziness
  • Headache
  • Mild rash
  • Trouble sleeping

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: September 18, 2013

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