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Important Note

The following information is intended to supplement, not substitute for, the expertise and judgment of your physician, pharmacist or other healthcare professional. It should not be construed to indicate that use of the drug is safe, appropriate, or effective for you. Consult your healthcare professional before using this drug.


(fen-ih-TOE-in, FEN-ih-toyn)



This medication is used to treat seizures and epilepsy.

How To Use

Use this medication as directed. Clean area before administering. Do not stop using this drug suddenly without consulting your doctor or seizures may occur. It is important to use all doses on time to keep the level of medication in your blood constant. Do this by using doses at evenly spaced intervals throughout the day and night. While using this medication, lab tests may be done, especially in the first few months, to check if the drug is working properly.

Side Effects

Pain at injection site, constipation, dizziness or drowsiness may occur. If these effects continue or worsen, inform your doctor. Unlikely but report: blurred vision, unsteadiness, nausea, mood changes or confusion, slurred speech, rash, insomnia, headache. Very unlikely but report: vomiting, stomach pain, uncoordinated movements, tingling in hands or feet, fever, yellowing of the eyes or skin, trouble breathing, swollen glands, sore throat, unusual bleeding or bruising. May cause enlargement of the gums. This can be minimized by maintaining good oral hygiene with regular brushing, flossing and massaging of the gums. If you notice other effects not listed above, contact your doctor or pharmacist.


Tell your doctor if you have: blood disorders (e.g., porphyria), allergies (especially drug allergies), lung problems, heart disease (including slow heart rate or heart blocks), liver disease. Use caution operating machinery or performing tasks requiring alertness. Limit alcohol use as it may increase the drowsiness effect of this medication. Limit your caffeine usage. Phenytoin is not recommended for use during pregnancy. Consult your doctor for details. This drug passes into breast milk. While there have been no reports of harm to a nursing infant, consult your doctor before breast-feeding.

Drug Interactions

Inform your doctor about all the medicine you use (both prescription and nonprescription) especially if you take: "blood thinners" (warfarin), cimetidine, omeprazole, sucralfate, disulfiram, oral antifungal medication (azoles), xanthine drugs to treat asthma (theophylline), isoniazid, folic acid, pyrimethamine, sulfa antibiotics, rifampin, trimethoprim, amiodarone, fluoxetine, anti-cancer drugs, valproic acid, divalproex, estrogens, disopyramide, levodopa (Sinemet), digoxin, felodipine, primidone, felbamate, narcotic pain medicines (e.g., codeine), St John's wort, capecitabine. This drug may interfere with the effectiveness of birth control pills. Discuss using other methods of birth control with your doctor. Do not start or stop any medicine without doctor or pharmacist approval.


If overdose is suspected, contact your local poison control center or emergency room immediately. Symptoms of overdose may include unusual eye movements, unsteadiness, nausea, dizziness, confusion, tremor, slurred speech, drowsiness, and loss of consciousness.


It is recommended to wear or carry medication identification indicating you are using this drug. Do not change from one brand of this product to another without consulting your doctor or pharmacist. Products made by different companies may not be equally effective.

Missed Dose

If you miss a dose, use it as soon as remembered; do not use if it is almost time for the next dose, instead, skip the missed dose and resume your usual dosing schedule. Do not "double-up" the dose to catch up.


Store at room temperature away from sunlight.

Medical Alert

Your condition can cause complications in a medical emergency. For enrollment information call MedicAlert at 1-800-854-1166 (USA), or 1-800-668-1507 (Canada).