Toggle navigation
Toggle search

Phenytoin (By mouth)

Phenytoin (FEN-i-toin)

Treats and prevents seizures.

Brand Name(s):

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

There may be other brand names for this medicine.

When This Medicine Should Not Be Used:

This medicine is not right for everyone. Do not use it if you had an allergic reaction to phenytoin or similar medicines, if you are pregnant, or if you have had liver problems from using phenytoin.

How to Use This Medicine:

Capsule, Long Acting Capsule, Liquid, Chewable Tablet

  • Take your medicine as directed. Your dose may need to be changed several times to find what works best for you.
  • You may take this medicine with food if it upsets your stomach. Take this medicine at the same time each day.
  • Capsule: Swallow whole. Do not open, crush, or chew it.
  • Chewable tablet: May be chewed, swallowed whole, or crushed before you swallow it.
  • Feeding tube: This medicine should be given at least 2 hours before or 2 hours after a feeding.
  • Oral liquid: Shake just before each use. Measure the oral liquid medicine with a marked measuring spoon, oral syringe, or medicine cup.
  • This medicine should come with a Medication Guide. Ask your pharmacist for a copy if you do not have one.
  • Missed dose: Take a dose as soon as you remember. If it is almost time for your next dose, wait until then and take a regular dose. Do not take extra medicine to make up for a missed dose.
  • Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Do not freeze the oral liquid.

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 affect how phenytoin works. There are many other drugs not listed. Make sure your doctor knows the names of all the medicines you use, especially the following:
    • Amiodarone, chloramphenicol, chlordiazepoxide, chlorpropamide, clozapine, cyclosporine, diazepam, diazoxide, digoxin, disopyramide, disulfiram, estrogen, fluvastatin, folic acid, furosemide, isoniazid, methadone, methylphenidate, mexiletine, praziquantel, quetiapine, reserpine, salicylates, St John's wort, sucralfate, theophylline, tolbutamide, trazodone, vitamin D
    • Blood thinner (including ticlopidine, warfarin)
    • Calcium channel blocker
    • Cancer medicine (including bleomycin, capecitabine, carboplatin, cisplatin, doxorubicin, fluorouracil, irinotecan, methotrexate, paclitaxel, teniposide)
    • HIV/AIDS medicine (including efavirenz, fosamprenavir, indinavir, lopinavir/ritonavir, nelfinavir, ritonavir, saquinavir)
    • Medicine to lower cholesterol (including atorvastatin, fluvastatin, simvastatin)
    • Medicine to treat depression (including fluoxetine, fluvoxamine, sertraline)
    • Medicine to treat infection (including albendazole, doxycycline, fluconazole, itraconazole, ketoconazole, miconazole, rifampin, sulfadiazine, sulfamethizole, sulfamethoxazole-trimethoprim, sulfaphenazole, voriconazole)
    • Muscle relaxant
    • Other medicines to treat seizures (including carbamazepine, ethosuximide, felbamate, oxcarbazepine, lamotrigine, methsuximide, oxcarbazepine, phenobarbital, topiramate, valproate sodium, valproic acid, vigabatrin)
    • Phenothiazine medicine
    • Stomach medicine (including cimetidine, omeprazole)
  • Do not take an antacid or supplement that contains calcium, aluminum, or magnesium at the same time you take phenytoin. Take the antacid or supplement at a different time of day.
  • If you are receiving tube feeding preparations, take this medicine before or after a feeding.
  • 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 disease, diabetes, porphyria, or a history of depression or mental problems.
  • This medicine may cause the following problems:
    • Increased risk of suicidal thoughts or behavior
    • Serious skin reactions (may happen after treatment has stopped)
    • Drug reaction with eosinophilia and systemic symptoms (DRESS), which may damage organs, including the liver, kidney, or heart
    • Heart problems (including slow heartbeat)
    • Liver problems
    • Lower bone density, which may lead to fractures
    • High blood sugar levels
  • This medicine may make you drowsy. Do not drive or do anything else that could be dangerous until you know how this medicine affects you.
  • This medicine may damage your gums. Brush and floss your teeth regularly and visit your dentist to help prevent these problems.
  • This medicine may make you bleed, bruise, or get infections more easily. Take precautions to prevent illness and injury. Wash your hands often.
  • 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.
  • Keep all medicine out of the reach of children. Never share your medicine with anyone.

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 urine or pale stools, nausea, vomiting, loss of appetite, stomach pain, yellow skin or eyes
  • Feeling depressed, irritable, or restless
  • Fever, chills, cough, sore throat, body aches
  • Fever, skin rash, or swollen glands in your armpits, neck, or groin
  • Severe confusion, problems with balance or walking, slurred speech, tremors
  • Slow heartbeat, chest pain or discomfort, lightheadedness, dizziness or fainting
  • Thoughts of hurting yourself, other unusual thoughts or behaviors
  • Unusual bleeding, bruising, or weakness

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.

All rights reserved

A.D.A.M. content is best viewed in IE9 or above, Firefox and chrome browser.

We are physicians, hospitals and communities working together to help you live better.