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 is not made to treat all types of seizures, and your doctor will determine if it is the right medication for you.
Phenytoin may also be used for other purposes not listed in this medication guide.
You should not use this medication if you are allergic to phenytoin.
If you have any of these other conditions, you may need a dose adjustment or special tests to safely use this medication:
- liver disease;
- diabetes; or
- a vitamin D deficiency or any other condition that causes thinning of the bones.
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.
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.
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.
Phenytoin can lower your blood sugar. If you are a diabetic, check your blood sugar regularly while you are taking this medication.
FDA pregnancy category D. This medication can cause harm to an unborn baby. Phenytoin may also not be as effective in reducing seizures if taken during pregnancy. Do not use phenytoin without your doctor’s consent if you are pregnant. Tell your doctor if you become pregnant during treatment. Use an effective form of birth control while you are using this medication.
Phenytoin can make birth control pills less effective. Use a non-hormonal form of birth control (such as a condom or diaphragm with spermicide) to prevent an unintended pregnancy.
Phenytoin can pass into breast milk and may harm a nursing baby. Do not use this medication without telling your doctor if you are breast-feeding a baby.
Avoid drinking alcohol. It can increase some of the side effects of phenytoin, and can also increase your risk of seizure.
Avoid taking antacids at the same time you take phenytoin. Antacids can make it harder for your body to absorb the medication.
Phenytoin can cause side effects that may impair your thinking or reactions. Be careful if you drive or do anything that requires you to be awake and alert.
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Seek emergency medical attention if you think you have used too much of this medicine. 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.
Take the missed dose as soon as you remember. If it is almost time for your next dose, skip the missed dose and take the medicine at your next regularly scheduled time. Do not take extra medicine to make up the missed dose.
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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.
Call your doctor at once if you have any new or worsening symptoms 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.
Call your doctor at once if you have any of these serious side effects:
- swollen glands, easy bruising or bleeding;, swollen or tender gums;
- fever, sore throat, and headache with a severe blistering, peeling, and red skin rash;
- confusion, hallucinations, unusual thoughts or behavior;
- slurred speech, loss of balance or coordination;
- tremor (uncontrolled shaking), restless muscle movements in your eyes, tongue, jaw, or neck;
- extreme thirst or hunger, urinating more than usual;
- loss of appetite, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes); or
- changes in the shape of your face or lips.
Less serious side effects may include:
- mild skin rash or itching;
- dizziness, nervousness, sleep problems (insomnia);
- nausea, vomiting, constipation; or
- headache, joint pain.
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.
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Drugs that can increase phenytoin levels in your blood include:
- stomach acid reducers such as cimetidine (Tagamet), ranitidine (Zantac), famotidine (Pepcid), or nizatidine (Axid);
- certain sedatives (such as Librium or Valium) or antidepressants (such as Prozac);
- estrogen hormone replacement;
- chlorpromazine (Thorazine), prochlorperazine (Compazine), thioridazine (Mellaril) and other phenothiazines;
- disulfiram (Antabuse);
- methylphenidate (Ritalin, Concerta, Daytrana); and
- sulfa drugs such as Septra or Bactrim.
Drugs that can make phenytoin less effective in controlling seizures include carbamazepine (Tegretol, Epitol, Carbatrol), sucralfate (Carafate), and molindone (Moban).
Other drugs that can interact with phenytoin include:
- phenobarbital (Luminal, Solfoton), valproic acid (Depakene) or divalproex sodium (Depakote);
- steroid medicines (prednisone and others);
- antidepressants such as amitriptyline (Elavil), clomipramine (Anafranil), imipramine (Janimine, Tofranil), paroxetine (Paxil), and others;
- antibiotics such as rifampin (Rimactane, Rifadin, Rifamate) or doxycycline (Doryx, Vibramycin, Adoxa, and others);
- digitoxin (digitalis, Lanoxin), furosemide (Lasix); and
- theophylline (Elixophyllin, Theo-Dur, Theo-Bid, Theolair, Uniphyl).
This list is not complete and there are many other medicines that can interact with phenytoin. Tell your doctor about all the prescription and over-the-counter medications you use. This includes vitamins, minerals, herbal products, and drugs prescribed by other doctors. Do not start using a new medication without telling your doctor. Keep a list with you of all the medicines you use and show this list to any doctor or other healthcare provider who treats you.
Di-Phen, Dilantin, Dilantin Infatabs, Dilantin Kapseals, Dilantin-125, Phenytek, Phenytoin Sodium, Prompt, and phenytoin
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