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Phenytoin (By mouth)

Phenytoin (FEN-i-toin)

Treats seizures. This medicine is an anticonvulsant.

Brand Name(s):

Dilantin, Dilantin Infatabs, Dilantin Kapseals, Dilantin-125, Diphen, Phenytek

There may be other brand names for this medicine.

When This Medicine Should Not Be Used:

Do not use this medicine if you have had an allergic reaction to phenytoin or similar medicines (such as Cerebyx®, Mesantoin®, Peganone®) or if you are pregnant. Do not use this medicine together with delavirdine (Rescriptor®).

How to Use This Medicine:

Capsule, Long Acting Capsule, Liquid, Chewable Tablet

  • Take your medicine as directed.
  • You may take this medicine with food if it upsets your stomach. Take this medicine at the same time each day.
  • Capsule: Swallow whole. Do not open, crush, or chew it.
  • Chewable tablet: May be chewed, swallowed whole, or crushed before you swallow it.
  • Oral liquid: Shake just before each use. Measure the oral liquid medicine with a marked measuring spoon, oral syringe, or medicine cup.
  • Feeding tube: This medicine should be given at least 2 hours before or 2 hours after a feeding.
  • This medicine should come with a Medication Guide. Ask your pharmacist for a copy if you do not have one.

If a dose is missed:

  • Take a dose as soon as you remember. If it is almost time for your next dose, wait until then and take a regular dose. Do not take extra medicine to make up for a missed dose.

How to Store and Dispose of This Medicine:

  • Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Do not freeze the oral liquid.
  • Ask your pharmacist, doctor, or health caregiver about the best way to dispose of any outdated medicine or medicine no longer needed.
  • Keep all medicine out of the reach of children. Never share your medicine with anyone.

Drugs and Foods to Avoid:

Ask your doctor or pharmacist before using any other medicine, including over-the-counter medicines, vitamins, and herbal products.

  • There are many other drugs that can interact with phenytoin. Make sure your doctor knows about all other medicines you are using.
  • Make sure your doctor knows if you are using other medicine for seizures, such as carbamazepine, ethosuximide, felbamate, methsuximide, oxcarbazepine, phenobarbital, quetiapine, valproate, topiramate, valproic acid, Depakene®, Tegretol®, Zarontin®).
  • Make sure your doctor knows if you also use St John's wort, amiodarone (Cordarone®), quinidine (Quinaglute®), aspirin, chlordiazepoxide (Librium®), cyclosporine (Gengraf®, Neoral®, Sandimmune®), diazepam (Valium®), digoxin (Lanoxin®), disulfiram (Antabuse®), folic acid, furosemide (Lasix®), isoniazid (Nydrazid®), methylphenidate (Ritalin®), nisoldipine (Sular®), praziquantel (Biltricide®), reserpine, sucralfate (Carafate®), theophylline (Theo-Dur®), tolbutamide (Orinase®), vitamin D, medicine to lower cholesterol (such as atorvastatin, fluvastatin, simvastatin), medicine to treat depression (such as fluoxetine, fluvoxamine, paroxetine, sertraline, trazodone), a phenothiazine medicine (such as promethazine, Phenergan®, Thorazine®), a stomach medicine (such as cimetidine, omeprazole, Tagamet®), or a blood thinner (such as warfarin, Coumadin®, Jantoven®).
  • Make sure your doctor knows if you also use cancer medicine (such as bleomycin, capecitabine, carboplatin, cisplatin, doxorubicin, fluorouracil, irinotecan, methotrexate, paclitaxel, teniposide, Camptosar®, Taxol®, Trexall®), medicine to treat an infection (such as chloramphenicol, doxycycline, fluconazole, itraconazole, ketoconazole, rifampin, voriconazole, Nizoral®), a sulfa drug (such as sulfamethoxazole/trimethoprim, sulfasalazine, Azulfidine®, Bactrim®, Septra®), a steroid medicine (such as hydrocortisone, methylprednisolone, prednisolone, prednisone), or medicine to treat HIV/AIDS (such as amprenavir, efavirenz, fosamprenavir, indinavir, lopinavir, nelfinavir, ritonavir, saquinavir, Kaletra®, Norvir®).
  • Do not take an antacid or supplement that contains calcium, aluminum, or magnesium (such as Maalox®, Mylanta®, Tums®) at the same time you take phenytoin. Take the antacid or supplement at a different time of day.
  • Birth control pills may not work well as well while you are taking phenytoin. To avoid pregnancy, use another form of birth control together with the pills.
  • Do not drink alcohol while you are using this medicine.

Warnings While Using This Medicine:

  • It is not safe to take this medicine during pregnancy. It could harm an unborn baby. Tell your doctor right away if you become pregnant.
  • Make sure your doctor knows if you are breastfeeding, or if you have kidney disease, liver disease, osteoporosis, diabetes, or porphyria.
  • Do not stop using this medicine suddenly. Your doctor will need to slowly decrease your dose before you stop it completely.
  • This medicine can increase thoughts of suicide. Although this is a risk for all patients, it is more likely in children, teenagers, and young adults. Tell your doctor right away if you feel depressed and have thoughts about hurting yourself. Report any unusual thoughts or behaviors that trouble you, especially if they are new or get worse quickly. Tell your doctor if you or anyone in your family has bipolar disorder (manic-depressive) or has tried to commit suicide.
  • Serious skin reactions can occur with this medicine. Check with your doctor right away if you have blisters, peeling skin, redness, skin rash, sores, fever, or chills. This is more likely to happen within the first month after you start using this medicine, but it can happen at any time.
  • Tell your doctor right away if you develop a fever, rash, and swollen or tender glands. Other symptoms might be unusual bleeding or bruising, or yellow eyes or skin. These may be symptoms of a serious and life-threatening reaction to this medicine.
  • This medicine may decrease bone mineral density. A low bone mineral density can cause weak bones or osteoporosis. Talk to your doctor if you have any questions about this.
  • This medicine may affect blood sugar levels. If you have diabetes and you notice a change in your blood sugar levels or if you have any questions, check with your doctor.
  • This medicine may make you drowsy. Do not drive, use machines, or do anything else that could be dangerous until you know how this medicine affects you.
  • This medicine may cause overgrowth of your gums. Brush and floss your teeth regularly and check with your dentist while taking this medicine to help prevent these problems.
  • Your doctor will do lab tests at regular visits to check on the effects of this medicine. Keep all appointments.
  • Tell any doctor or dentist who treats you that you are using this medicine. This medicine may affect certain medical test results.

Possible Side Effects While Using This Medicine:

Call your doctor right away if you notice any of these side effects:

  • Allergic reaction: Itching or hives, swelling in your face or hands, swelling or tingling in your mouth or throat, chest tightness, trouble breathing
  • Blistering, peeling, or red skin rash
  • Dark-colored urine or pale stools, nausea, vomiting, loss of appetite, pain in your upper stomach, yellow skin or eyes
  • Feeling depressed, irritable, or restless
  • Fever, chills, cough, sore throat, and body aches
  • Severe confusion, problems with balance or walking, slurred speech, tremors
  • Swollen glands in your armpits, neck, or groin
  • Unusual bleeding, bruising, or weakness
  • Unusual thoughts or behaviors, thoughts of hurting yourself

If you notice these less serious side effects, talk with your doctor:

  • Constipation, nausea, vomiting
  • Mild confusion, slurred speech, clumsiness, problems with balance
  • Dizziness, headache
  • Mild rash

If you notice other side effects that you think are caused by this medicine, tell your doctor

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


Last Updated: 4/4/2014

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