Phenytoin is used to prevent and control seizures (also called an anticonvulsant or antiepileptic drug). It works by reducing the spread of seizure activity in the brain.

OTHER USES: This section contains uses of this drug that are not listed in the approved professional labeling for the drug but that may be prescribed by your health care professional. Use this drug for a condition that is listed in this section only if it has been so prescribed by your health care professional.

This drug may also be used to treat certain types of irregular heartbeats and painful nerve conditions (e.g., trigeminal neuralgia).

Shake the bottle well before each dose. Take this medication by mouth usually 2 or 3 times a day, or as directed by your doctor. This product is not recommended for use once a day. You may take it with food if stomach upset occurs.

Use this medication regularly in order to get the most benefit from it. It is important to take all doses on time to keep the amount of medicine in your body at a constant level. Remember to use it at the same times each day. Dosage is based on your medical condition and response to therapy.

Products that contain calcium (e.g., antacids, calcium supplements) and nutritional tube-feeding (enteral) products may decrease the absorption of phenytoin. If you are using any such products, separate taking them from phenytoin by at least 2 hours.

Do not stop taking this medication without consulting your doctor. Seizures may become worse when the drug is suddenly stopped. Your dose may need to be gradually decreased.

Inform your doctor if your condition does not improve or worsens.

Headache, nausea, vomiting, constipation, dizziness, drowsiness, trouble sleeping, or nervousness may occur. If any of these effects persist or worsen, notify your doctor or pharmacist promptly.

Phenytoin may cause swelling and bleeding of the gums. Massage your gums and brush and floss your teeth regularly to minimize this problem. See your dentist regularly.

Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

Tell your doctor immediately if any of these unlikely but serious side effects occur: unusual eye movements, loss of coordination, slurred speech, confusion, muscle twitching, double or blurred vision, tingling of the hands/feet, facial changes (e.g., swollen lips, butterfly-shaped rash around the nose/cheeks), excessive hair growth, increased thirst or urination, unusual tiredness, bone or joint pain, easily broken bones.

This medication rarely may cause mood or behavior changes, such as anxiety, agitation, hostility, pressured/rapid speech, or thoughts of suicide. Tell your doctor immediately if you develop unusual (possibly sudden) mood changes.

For males, in the very unlikely event you have a painful or prolonged erection lasting 4 or more hours, stop using this drug and seek immediate medical attention, or permanent problems could occur.

Tell your doctor immediately if any of these highly unlikely but very serious side effects occur: uncontrolled muscle movements, swollen glands (lymph nodes), stomach/abdominal pain, persistent nausea/vomiting, yellowing eyes or skin, dark urine, easy bruising/bleeding, signs of infection (e.g., persistent sore throat or fever).

A serious allergic reaction to this drug is unlikely, but seek immediate medical attention if it occurs. Symptoms of a serious allergic reaction include: rash, high fever, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing.

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.

In the US -

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

Before taking phenytoin, tell your doctor or pharmacist if you are allergic to it; or to other anti-seizure medications (e.g., ethotoin, phenobarbital, ethosuximide, trimethadione); or if you have any other allergies.

Before using this medication, tell your doctor or pharmacist your medical history, especially of: alcohol use, certain blood conditions (porphyria), diabetes, liver disease, lupus, folate or vitamin B-12 deficiency (megaloblastic anemia).

This drug may make you dizzy or drowsy. Do not drive, use machinery, or do any activity that requires alertness until you are sure you can perform such activities safely. Limit alcoholic beverages. Alcohol may also affect your blood levels of this drug.

Tell your doctor you are using phenytoin prior to surgery or any procedure that makes you unable to take it by mouth.

If you have diabetes, this drug may increase your blood sugar levels. Check your blood (or urine) glucose level frequently, as directed by your doctor. Promptly report any abnormal results as directed. Your medicine, exercise plan, or diet may need to be adjusted.

Vitamin D supplements may be necessary to prevent weakening of the bones (osteomalacia). Discuss this with your doctor.

This medication is not recommended for use during pregnancy due to the possible risk of birth defects and harm to an unborn baby. Consult your doctor for more details.

Phenytoin passes into breast milk. Consult your doctor before breast-feeding.

Your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor or pharmacist first.

See also How to Use section.

This drug should not be used with the following medications because very serious interactions may occur: azapropazone, darunavir, delavirdine, dofetilide, etravirine, nisoldipine, telithromycin.

If you are currently using any of these medications, tell your doctor or pharmacist before starting phenytoin.

Before using this medication, tell your doctor or pharmacist of all prescription and nonprescription/herbal products you may use, especially of: colesevelam, molindone, pyridoxine (vitamin B6), sucralfate, sulfa drugs, drugs affecting liver enzymes that remove phenytoin from your body (such as amiodarone, azole antifungals including itraconazole, cimetidine, ciprofloxacin, macrolide antibiotics including erythromycin, estrogens, isoniazid, rifamycins including rifabutin, St. John's wort, other anti-seizure medicines including carbamazepine/phenobarbital/valproic acid).

Phenytoin can speed up the removal of many other drugs from your body by affecting certain liver enzymes. This can affect how well these other drugs work. These other drugs include: some drugs to treat cancer (e.g., imatinib, irinotecan), corticosteroids (e.g., prednisone), cyclosporine, felodipine, quetiapine, quinidine, theophylline, vitamin D, warfarin. This is not a complete list. Tell your doctor or pharmacist of all other drugs you take.

Also report the use of drugs which might increase seizure risk (decrease seizure threshold) such as: phenothiazines (e.g., thioridazine) or tricyclic antidepressants (e.g., amitriptyline), among others. Consult your doctor or pharmacist for details.

Phenytoin may decrease the effectiveness of birth control pills, patches, implants or injections. This can result in pregnancy. You may need to use an additional form of reliable birth control while using this medication. Consult your doctor or pharmacist for details.

This product can affect the results of certain lab tests. Make sure laboratory personnel and your doctors know you use this drug.

This document does not contain all possible interactions. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you, and share the list with your doctor and pharmacist.

If overdose is suspected, contact your local poison control center or emergency room immediately. US residents can call the US national poison hotline at 1-800-222-1222. Canadian residents should call their local poison control center directly. Symptoms of overdose may include: severe mental/mood changes, severe drowsiness, loss of consciousness, slowed breathing.

Do not share this medication with others.

Laboratory and/or medical tests (e.g., phenytoin blood levels, liver function tests) should be performed periodically to monitor your progress or check for side effects. Consult your doctor for more details.

Do not change from one brand of this product to another, or to another dose form of this drug (e.g., capsules) without consulting your doctor or pharmacist. Your dosage may have to be adjusted.

If you miss a dose, use it as soon as you remember 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 between 68-77 degrees F (20-25 degrees C) away from light and moisture. Do not freeze. Do not store in the bathroom. Keep all medicines away from children and pets.

Do not flush medications down the toilet or pour them into a drain unless instructed to do so. Properly discard this product when it is expired or no longer needed. Consult your pharmacist or local waste disposal company for more details about how to safely discard your product.

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).

Information last revised April 2009 Copyright(c) 2009 First DataBank, Inc.