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phenytoin (oral)

Pronunciation: FEN i toyn

Brand: Dilantin, Dilantin Infatabs, Dilantin-125, Phenytek

Dilantin 100 mg

capsule, orange/white, imprinted with DILANTIN, 100 mg

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Dilantin 100 mg-NEW

capsule, orange/white, imprinted with PD, DILANTIN 100 mg

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Dilantin 30 mg

pink/white, imprinted with P-D 365

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Dilantin 50 mg

triangular, yellow, imprinted with P-D 007

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Phenytek 200 mg-MYL

dark blue/blue, imprinted with BERTEK 670

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Phenytek 300 mg-MYL

blue, imprinted with BERTEK 750, BERTEK 750

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Phenytoin ER 100 mg-AMN

capsule, purple/white, imprinted with IP 212

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Phenytoin ER 100 mg-MYL

capsule, purple/white, imprinted with BERTEK 560

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What is the most important information I should know about phenytoin?

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You should not use phenytoin if you also take delavirdine (Rescriptor), or if you are allergic to phenytoin, ethotoin (Peganone), fosphenytoin (Cerebyx), or mephenytoin (Mesantoin).

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If you are pregnant, DO NOT START TAKING phenytoin unless your doctor tells you to. Phenytoin may cause harm to an unborn baby, but having a seizure during pregnancy could harm both the mother and the baby. If you become pregnant while taking phenytoin, DO NOT STOP TAKING the medicine without your doctor's advice. Seizure control is very important during pregnancy and the benefits of preventing seizures may outweigh any risks posed by using phenytoin.

You may have thoughts about suicide while taking this medication. Your doctor will need to check you at regular visits. Do not miss any scheduled appointments.

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Report any new or worsening symptoms to your doctor, such as: mood or behavior changes, depression, anxiety, or if you feel agitated, hostile, restless, hyperactive (mentally or physically), or have thoughts about suicide or hurting yourself.

What is phenytoin?

Phenytoin is an anti-epileptic drug, also called an anticonvulsant. It works by slowing down impulses in the brain that cause seizures.

Phenytoin is used to control seizures. Phenytoin does not treat all types of seizures, and your doctor will determine if it is the right medication for you.

Phenytoin may also be used for purposes not listed in this medication guide.

What should I discuss with my healthcare provider before taking phenytoin?

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You should not use phenytoin if you also take delavirdine (Rescriptor), or if you are allergic to phenytoin, ethotoin (Peganone), fosphenytoin (Cerebyx), or mephenytoin (Mesantoin).

To make sure you can safely take phenytoin, tell your doctor if you have any of these other conditions:

  • liver disease;
  • lupus;
  • diabetes;
  • a vitamin D deficiency or any other condition that causes thinning of the bones;
  • porphyria (a genetic enzyme disorder that causes symptoms affecting the skin or nervous system); or
  • if you drink large amounts of alcohol.

Your family or other caregivers should also be alert to changes in your mood or symptoms. Your doctor will need to check you at regular visits. Do not miss any scheduled appointments.

You may have thoughts about suicide while taking this medication. Tell your doctor if you have new or worsening depression or suicidal thoughts during the first several months of treatment, or whenever your dose is changed.

Patients of Asian ancestry may have a higher risk of developing a rare but serious skin reaction to phenytoin. Your doctor may recommend a blood test before you start the medication to determine your risk of this skin reaction.

FDA pregnancy category D. Phenytoin may cause harm to an unborn baby, but having a seizure during pregnancy could harm both the mother and the baby.

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If you are pregnant, DO NOT START TAKING phenytoin unless your doctor tells you to. If you become pregnant while taking phenytoin, DO NOT STOP TAKING the medicine without your doctor's advice.

Seizure control is very important during pregnancy. The benefit of preventing seizures may outweigh any risks posed by taking phenytoin. Follow your doctor's instructions about taking phenytoin while you are pregnant.

Phenytoin can make birth control pills less effective. To prevent pregnancy while you are taking phenytoin, use a non-hormonal form of birth control (such as a condom or diaphragm with spermicide).

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Phenytoin can pass into breast milk and may harm a nursing baby. You should not breast-feed while you are using phenytoin.

How should I take phenytoin?

Take exactly as prescribed by your doctor. Do not take in larger or smaller amounts or for longer than recommended. Follow the directions on your prescription label.

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Do not crush, chew, break, or open an extended-release capsule. Swallow it whole. Breaking or opening the pill may cause too much of the drug to be released at one time. Do not use any phenytoin capsule that has changed colors. Call your doctor for a new prescription.

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Shake the oral suspension (liquid) well just before you measure a dose. Measure the liquid with a special dose-measuring spoon or medicine cup, not with a regular table spoon. If you do not have a dose-measuring device, ask your pharmacist for one.

To be sure this medication is helping your condition, your blood may need to be tested often. You may also need a blood test when switching from one form of phenytoin to another. Visit your doctor regularly.

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If you are taking phenytoin to treat seizures, keep taking the medication even if you feel fine. You may have an increase in seizures if you stop taking phenytoin. Do not change your dose of phenytoin without your doctor's advice. Tell your doctor if the medication does not seem to work as well in treating your condition.

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Wear a medical alert tag or carry an ID card stating that you take phenytoin. Any medical care provider who treats you should know that you are taking a seizure medication.

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Store at room temperature away from moisture, light, and heat.

What happens if I miss a dose?

Take the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose.

What happens if I overdose?

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Seek emergency medical attention or call the Poison Help line at 1-800-222-1222. An overdose of phenytoin can be fatal. Overdose symptoms may include twitching eye movements, slurred speech, loss of balance, tremor, muscle stiffness or weakness, nausea, vomiting, feeling light-headed, fainting, and slow or shallow breathing.

What should I avoid while taking phenytoin?

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Avoid drinking alcohol while you are taking phenytoin. Alcohol use can increase your blood levels of phenytoin and may increase side effects. Daily alcohol use can decrease your blood levels of phenytoin, which can increase your risk of seizures.

Avoid taking antacids at the same time you take phenytoin. Antacids can make it harder for your body to absorb the medication.

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Phenytoin may impair your thinking or reactions. Be careful if you drive or do anything that requires you to be alert.

What are the possible side effects of phenytoin?

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Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat. You may be more likely to have an allergic reaction if you are African-American.

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Report any new or worsening symptoms to your doctor, such as: mood or behavior changes, depression, anxiety, or if you feel agitated, hostile, restless, hyperactive (mentally or physically), or have thoughts about suicide or hurting yourself.

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Call your doctor at once if you have a serious side effect such as:

  • fever, swollen glands, body aches, flu symptoms;
  • skin rash, easy bruising or bleeding, severe tingling, numbness, pain, muscle weakness;
  • upper stomach pain, loss of appetite, dark urine, jaundice (yellowing of the skin or eyes);
  • chest pain, irregular heart rhythm, feeling short of breath;
  • confusion, nausea and vomiting, swelling, rapid weight gain, urinating less than usual or not at all;
  • new or worsening cough with fever, trouble breathing;
  • tremor (uncontrolled shaking), restless muscle movements in your eyes, tongue, jaw, or neck;
  • patchy skin color, red spots, or a butterfly shaped skin rash over your cheeks and nose (worsens in sunlight); or
  • severe skin reaction -- fever, sore throat, swelling in your face or tongue, burning in your eyes, skin pain, followed by a red or purple skin rash that spreads (especially in the face or upper body) and causes blistering and peeling.

Less serious side effects may include:

  • slurred speech, loss of balance or coordination;
  • swollen or tender gums; or
  • headache, dizziness, nervousness, or sleep problems (insomnia).

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

What other drugs will affect phenytoin?

Many drugs can interact with phenytoin. Below is just a partial list. Tell your doctor if you are using:

  • antibiotics such as cycloserine (Seromycin), doxycycline (Doryx, Vibramycin, Adoxa), isoniazid (for treating tuberculosis), linezolid (Zyvox), rifampin (Rimactane, Rifadin, Rifamate), or sulfa drugs (Bactrim, Septra, Sulfatrim, SMX-TMP, and others);
  • an antidepressant (such as Elavil, Vanatrip, Limbitrol, Sinequan, Silenor, Pamelor, Paxil, Zoloft, Desyrel, and others);
  • aspirin or other salicylates;
  • birth control pills or hormone replacement therapy;
  • a blood thinner such as warfarin (Coumadin, Jantoven);
  • certain sedatives (Librium, Librax, Limbitrol, Valium) or antidepressants (Desyrel, Luvox, Zoloft, Prozac, Rapiflux, Sarafem, Selfemra, Symbyax);
  • heart medication such as amiodarone (Cordarone, Pacerone), digoxin (digitalis, Lanoxin), furosemide (Lasix), or quinidine (Quin-G);
  • prochlorperazine (Compazine, Compro), promethazine (Pentazine, Phenergan, Anergan, Antinaus), and other phenothiazines;
  • steroid medicines (prednisone and others);
  • seizure medicine (such as Carbatrol, Equetro, Tegretol, Solfoton, Depakene, or Depakote);
  • stomach acid reducers (such Tagamet, Prilosec, Zegerid, Zantac, Pepcid, or Axid); or
  • theophylline (Elixophyllin, Theo-Dur, Theo-Bid, Theolair, Uniphyl).
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This list is not complete and there are many other medicines that can interact with phenytoin. Tell your doctor about all medications you use. This includes prescription, over-the-counter, vitamin, and herbal products. Do not start a new medication without telling your doctor. Keep a list of all your medicines and show it to any healthcare provider who treats you.

Where can I get more information?

Your pharmacist can provide more information about phenytoin.


Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.

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