Phenytoin Capsules

Phenytoin is a medication that calms overactive nerves in your body. It helps treat symptoms of epilepsy by preventing and regulating seizures. It can also prevent seizures after brain surgery. Phenytoin comes in a capsule that you can take by mouth with a glass of water. The brand names of this medication are Dilantin® and Phenytek®.

What is this medication?

PHENYTOIN (FEN i toyn) prevents and controls seizures in people with epilepsy. It may also be used to prevent and treat seizures during or after brain surgery. It works by calming overactive nerves in your body.

This medicine may be used for other purposes; ask your health care provider or pharmacist if you have questions.

COMMON BRAND NAME(S): Dilantin, Phenytek


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What should I tell my care team before I take this medication?

They need to know if you have any of these conditions:

  • An alcohol abuse problem
  • Asian ancestry
  • Blood disorders or disease
  • Diabetes
  • Heart problems
  • Kidney disease
  • Liver disease
  • Porphyria
  • Receiving radiation therapy
  • Suicidal thoughts, plans, or attempt; a previous suicide attempt by you or a family member
  • Thyroid disease
  • An unusual or allergic reaction to phenytoin, other medications, foods, dyes, or preservatives
  • Pregnant or trying to get pregnant
  • Breast-feeding

How should I use this medication?

Take this medication by mouth with water. Take it as directed on the prescription label at the same time every day. Do not cut, crush or chew this medication. Swallow the capsules whole. You can take it with or without food. You should always take it the same way. Keep taking it unless your care team tells you to stop.

A special MedGuide will be given to you by the pharmacist with each prescription and refill. Be sure to read this information carefully each time.

Talk to your care team about the use of this medication in children. While it may be prescribed for to children for selected conditions, precautions do apply.

Overdosage: If you think you have taken too much of this medicine contact a poison control center or emergency room at once.

NOTE: This medicine is only for you. Do not share this medicine with others.


What if I miss a dose?

If you miss a dose, take it as soon as you can. If it is almost time for your next dose, take only that dose. Do not take double or extra doses.

What may interact with this medication?

Do not take this medication with any of the following:

  • Artemether
  • Certain antivirals for HIV or hepatitis
  • Idelalisib
  • Isavuconazonium
  • Lonafarnib
  • Lorlatinib
  • Lumefantrine
  • Lurasidone
  • Pacritinib
  • Praziquantel
  • Ranolazine

This medication may also interact with the following:

  • Albendazole
  • Alcohol
  • Aspirin and aspirin-like medications
  • Bleomycin
  • Capecitabine
  • Carboplatin
  • Certain medications for blood pressure, heart disease, irregular heart beat
  • Certain medications for depression, anxiety, or psychotic disorders
  • Certain medications for cholesterol like atorvastatin, fluvastatin, simvastatin
  • Certain medications for fungal infections like fluconazole, itraconazole, ketoconazole, miconazole, posaconazole, voriconazole
  • Certain medications for seizures like carbamazepine, ethosuximide, felbamate, lacosamide, lamotrigine, methsuximide, oxcarbazepine, phenobarbital, topiramate, valproic acid, vigabatrin
  • Certain medications for stomach problems like antacids, cimetidine, omeprazole, sucralfate
  • Certain medications that treat or prevent blood clots like warfarin, apixaban, dabigatran, edoxaban, and rivaroxaban
  • Chloramphenicol
  • Chlorpropamide
  • Cisplatin
  • Cyclosporine
  • Disulfiram
  • Doxorubicin
  • Doxycycline
  • Female hormones, like estrogen and birth control pills
  • Fluorouracil
  • Folic acid
  • Irinotecan
  • Isoniazid
  • Medications that relax muscles for surgery
  • Methadone
  • Methotrexate
  • Methylphenidate
  • Paclitaxel
  • Phenothiazines like chlorpromazine, mesoridazine, prochlorperazine, thioridazine
  • Rifampin
  • St. John's Wort
  • Steroid medications like prednisone or cortisone
  • Sulfadiazine
  • Sulfamethoxazole
  • Teniposide
  • Theophylline
  • Ticagrelor
  • Ticlopidine
  • Tolbutamide
  • Vitamin D

This list may not describe all possible interactions. Give your health care provider a list of all the medicines, herbs, non-prescription drugs, or dietary supplements you use. Also tell them if you smoke, drink alcohol, or use illegal drugs. Some items may interact with your medicine.


What should I watch for while using this medication?

Visit your care team for regular checks on your progress. This medication needs careful monitoring. Your care team may schedule regular blood tests.

This medication may cause serious skin reactions. They can happen weeks to months after starting the medication. Contact your care team right away if you notice fevers or flu-like symptoms with a rash. The rash may be red or purple and then turn into blisters or peeling of the skin. Or, you might notice a red rash with swelling of the face, lips or lymph nodes in your neck or under your arms.

Wear a medical ID bracelet or chain, and carry a card that describes your disease and details of your medication and dosage times.

Do not change brands or dosage forms of this medication without discussing the change with your care team.

You may get drowsy or dizzy. Do not drive, use machinery, or do anything that needs mental alertness until you know how this medication affects you. Do not stand or sit up quickly, especially if you are an older patient. This reduces the risk of dizzy or fainting spells. Alcohol may interfere with the effect of this medication. Avoid alcoholic drinks.

Birth control pills may not work properly while you are taking this medication. Talk to your care team about using an extra method of birth control.

This medication can cause unusual growth of gum tissues. Visit your dentist regularly. Problems can arise if you need dental work, and in the day-to-day care of your teeth. Try to avoid damage to your teeth and gums when you brush or floss your teeth.

Do not take antacids at the same time as this medication. If you get an upset stomach and want to take an antacid or medication for diarrhea, make sure there is an interval of 2 to 3 hours before or after you took your phenytoin.

The use of this medication may increase the chance of suicidal thoughts or actions. Pay special attention to how you are responding while on this medication. Any worsening of mood, or thoughts of suicide or dying should be reported to your care team right away.

Women who become pregnant while using this medication may enroll in the North American Antiepileptic Drug Pregnancy Registry by calling 1-888-233-2334. This registry collects information about the safety of antiepileptic medication use during pregnancy.

This medication may cause a decrease in vitamin D and folic acid. You should make sure that you get enough vitamins while you are taking this medication. Discuss the foods you eat and the vitamins you take with your care team.

What side effects may I notice from receiving this medication?

Side effects that you should report to your care team as soon as possible:

  • Allergic reactions—skin rash, itching, hives, swelling of the face, lips, tongue, or throat
  • High blood sugar (hyperglycemia)—increased thirst or amount of urine, unusual weakness or fatigue, blurry vision
  • Infection—fever, chills, cough, or sore throat
  • Liver injury—right upper belly pain, loss of appetite, nausea, light-colored stool, dark yellow or brown urine, yellowing skin or eyes, unusual weakness or fatigue
  • Phenytoin toxicity—uncontrollable eye movements, loss of balance or coordination, trouble speaking, unusual weakness or fatigue, nausea, vomiting
  • Rash, fever, and swollen lymph nodes
  • Redness, blistering, peeling, or loosening of the skin, including inside the mouth
  • Slow heartbeat—dizziness, feeling faint or lightheaded, confusion, trouble breathing, unusual weakness or fatigue
  • Swollen lymph nodes in the neck, groin, chest, or underarm area
  • Thoughts of suicide or self-harm, worsening mood, or feelings of depression
  • Unusual bruising or bleeding

Side effects that usually do not require medical attention (report to your care team if they continue or are bothersome):

  • Difficulty with paying attention, memory, or speech
  • Dizziness
  • Drowsiness
  • Headache

This list may not describe all possible side effects. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Where should I keep my medication?

Keep out of the reach of children.

Store at room temperature between 15 and 30 degrees C (59 and 86 degrees F). Protect from light and moisture. Throw away any unused medication after the expiration date.

NOTE: This sheet is a summary. It may not cover all possible information. If you have questions about this medicine, talk to your doctor, pharmacist, or health care provider.

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