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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-eh-TOE-in, FEN-eh-toyn)



This medication is used to treat seizures and epilepsy.

How To Use

Take with food or milk if stomach upset occurs. Take this medication with a full glass (8 oz or 240 ml) of water unless your doctor directs you otherwise. Do not lie down for 30 minutes after taking this medication. Capsules should be swallowed whole unless otherwise directed. Chewable tablets must be chewed thoroughly before swallowing. The suspension must be shaken well before measuring each dose. This medication must be taken as prescribed. Do not stop taking this drug suddenly without consulting your doctor as seizures may occur. It is important to take all doses on time to keep the level of medication in your blood constant. Do this by taking doses at the same time(s) each day. Do not skip doses.

Side Effects

Constipation, dizziness and 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, 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. In the unlikely event you have an allergic reaction to this drug, seek immediate medical attention. Symptoms of an allergic reaction include: rash, itching, swelling, dizziness, trouble breathing. If you notice other effects not listed above, contact your doctor or pharmacist.


Tell your doctor your medical history, especially of: blood disorders (e.g., porphyria), allergies (especially drug allergies), liver disease. Use caution operating machinery or performing tasks requiring alertness if this medication makes you dizzy or drowsy. 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 before taking this drug. This drug is excreted into breast milk. Consult your doctor before breast-feeding.

Drug Interactions

Inform your doctor of all the medicines you may use (both prescription and nonprescription), especially of: warfarin, cimetidine, omeprazole, sucralfate, disulfiram, oral antifungal medication (azoles), xanthine drugs (e.g., theophylline), isoniazid, folic acid, pyrimethamine, sulfa antibiotics, birth control pills, rifampin, trimethoprim, amiodarone, fluoxetine, anticancer drugs, valproic acid or divalproex, estrogens, disopyramide, levodopa, felodipine, primidone, felbamate, digoxin, metyrapone, dopamine, St John's wort, chloramphenicol, phenylbutazone, quinidine, doxycycline, diazoxide, cyclosporine, corticosteroids (e.g., prednisone, hydrocortisone), narcotic pain medicines (e.g., codeine), capecitabine. Phenytoin 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.


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. Lab tests may be done to monitor your progress.

Missed Dose

If you miss a dose and take 1 dose daily: take as soon as remembered unless you do not remember until the next day. In that case, skip the missed dose and resume your usual dosing schedule the following day. If you take several doses daily and should miss a dose: take as soon as remembered unless it is within 4 hours of the next dose. In that case, skip the missed dose and resume your usual schedule. Check with your doctor if you miss doses for more than 2 days in a row. Do not double the dose to catch up.


Store at room temperature away from moisture and sunlight. Do not store in the bathroom.

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).