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Drug Profile

The information on this site is intended to supplement and enhance, not replace, the advice of a physician who is familiar with your medical history. Decisions about your health should always be made ONLY after detailed conversation with your doctor.

Generic drug name: phenytoin (FEN i toyn)
GENERIC: available FAMILY: Drugs for Epilepsy
Find the drug label by searching at DailyMed.

Pregnancy and Breast-feeding Warnings [top]

Pregnancy Warning

Phenytoin has caused serious harm to human infants born to mothers taking this drug during pregnancy. Such infants have been born with cleft palate, damage to the heart, a small head, and mental deficiency. There have been reports of cancer in children whose mothers took phenytoin during pregnancy. Because of the potential for serious adverse effects to the fetus, this drug should not be used by pregnant women.

Breast-feeding Warning

Phenytoin is excreted in human milk. Because of the potential for serious adverse effects in nursing infants, you should not take this drug while nursing.

Facts About This Drug [top]

Phenytoin (DILANTIN) is approved by the Food and Drug Administration (FDA) to treat most forms of epilepsy. Patients taking phenytoin should adhere strictly to the prescribed dosing schedule and inform the prescribing physician of any situation in which it is not possible to take the drug as prescribed (for example, before, during or after surgery). Sudden discontinuation of the drug or rapid dosage reduction can result in status epilepticus, a medical emergency characterized by prolonged...

Phenytoin (DILANTIN) is approved by the Food and Drug Administration (FDA) to treat most forms of epilepsy. Patients taking phenytoin should adhere strictly to the prescribed dosing schedule and inform the prescribing physician of any situation in which it is not possible to take the drug as prescribed (for example, before, during or after surgery). Sudden discontinuation of the drug or rapid dosage reduction can result in status epilepticus, a medical emergency characterized by prolonged seizures.

Adverse effects[1]

Phenytoin can cause severe, sometimes fatal skin adverse reactions (including Stevens-Johnson syndrome and toxic epidermal necrolysis). Certain patients of Asian ancestry are at greatest risk of these adverse events. Patients should notify their physicians immediately if a skin rash develops while taking phenytoin.

Epilepsy drugs, including phenytoin, increase the risk of suicidal thoughts or behavior. Patients using these drugs should be monitored for new onset or worsening of depression, suicidal thoughts or behavior, or any unusual changes in mood or behavior.

A condition known as Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS) has been reported in patients using phenytoin. DRESS is also known as multi-organ hypersensitivity and in some cases has been fatal. Symptoms of DRESS include fever, rash, swollen lymph nodes and facial swelling. The disorder can cause inflammation of the liver, kidneys, heart and muscles.

Cases of abnormally slow heart rate and cardiac arrest have been reported in patients treated with phenytoin. Most of the cases of cardiac arrest occurred in patients who already had heart disease.

Chronic use of phenytoin has been associated with decreased bone mineral density (osteopenia, osteoporosis and osteomalacia) and bone fractures. Importantly, the drug can decrease vitamin D levels, which may lead to vitamin D deficiency.

Before You Use This Drug [top]

Do not use if you have or have had:

  • heart disease

Tell your doctor if you have or have had:

  • allergies to drugs
  • pregnancy or are breast-feeding
  • alcohol dependence
  • blood cell abnormalities
  • diabetes
  • fever above 101A1F for longer than 24 hours
  • liver problems
  • heart or blood vesssel disease
  • porphyria
  • kidney problems
  • thyroid problems
  • systemic lupus erythematosus

Tell your doctor about any other drugs you take, including aspirin, herbs, vitamins, and other nonprescription products.

When You Use This Drug [top]

  • Schedule regular visits with your doctor to check your progress.
  • Check with your doctor before taking other drugs.
  • Until you know how you react to this drug, do not drive or perform other activities requiring alertness. Phenytoin can cause dizziness, blurred vision, drowsiness, and lack of muscle coordination.
  • Do not drink alcohol.
  • Do not take this drug within two to three hours of taking an antacid or drug for diarrhea.
  • Do not change brands or dosage forms of this drug without checking with your doctor.
  • Do not suddenly stop taking this drug without checking with your doctor to find out if you need to taper off the drug.
  • Schedule frequent visits with your dentist to have your teeth cleaned, to prevent enlarged, tender, and bleeding gums.
  • Wear a medical identification bracelet or carry a card stating that you take phenytoin.
  • There is a possible interference with some laboratory tests.
  • If you plan to have any surgery, including dental, tell your doctor that you take this drug.
  • If using oral contraceptives, use a different or additional birth control method.

How to Use This Drug [top]

  • Do not share your medication with others.
  • Take the drug at the same time(s) each day.
  • If you miss a dose and you are supposed to take the drug once a day, take as soon as possible unless it is the next day, then continue on schedule. Do not take double doses.
  • If you are supposed to take the drug several times a day, take the missed dose as soon as possible unless within four hours of next scheduled dose, then continue on regular schedule. Do not take double doses. Check with your doctor if doses are missed for two or more days in a row.
  • Take with food.
  • Store at room temperature with lid on tightly. Do not store in the bathroom. Do not expose to heat, moisture, or strong light. Keep out of reach of children.
  • For liquid dosage form: Shake well and use an accurate measuring spoon, a plastic syringe, or a small graduated cup.
  • For chewable tablets: Chew or crush tablets or swallow them whole.
  • For capsules: Swallow capsule whole.

Interactions with Other Drugs [top]

The following drugs, biologics (e.g., vaccines, therapeutic antibodies), or foods are listed in Evaluations of Drug Interactions 2003 as causing “highly clinically significant” or “clinically significant” interactions when used together with any of the drugs in this section. In some sections with multiple drugs, the interaction may have been reported for one but not all drugs in this section, but we include the interaction because the drugs in this section are similar to one another. We have also included potentially serious interactions listed in the drug’s FDA-approved professional package insert or in published medical journal articles. There may be other drugs, especially those in the families of drugs listed below, that also will react with this drug to cause severe adverse effects. Make sure to tell your doctor and pharmacist the drugs you are taking and tell them if you are taking any of these interacting drugs:

8-MOP, ADALAT, ADALAT CC, ADVIL, AGENERASE, alcohol, ALERMINE, allopurinol, amiodarone, amprenavir, ANTABUSE, azapropazone, BICNU, CALCIFEROL, CAMPTOSAR, CARAFATE, carmustine, charcoal, chloramphenicol, CHLOROMYCETIN, chlorpheniramine, CHLOR-TRIMETON, cimetidine, CIPRO, ciprofloxacin, clopidogrel, CORDARONE, cyclosporine, DECADRON, delavirdine, DEPAKENE/DEPAKOTE, dexamethasone, diazoxide, dicumarol, DIFLUCAN, digitalis, digoxin, disopyramide, disulfiram, divalproex/valproic acid, dopamine, doxycycline, DURAQUIN, ELIXOPHYLLIN, ergocalciferol, felbamate, FELBATOL, fluconazole, fluoxetine, folic acid, FOLICET, FOLVITE, FORTOVASE, GABITRIL, GANTANOL, GLUCOPHAGE, HEXADROL, ibuprofen, INH, INTROPIN, INVIRASE, irinotecan, isoniazid, ketorolac, LANOXICAPS, LANOXIN, metformin, methotrexate, methoxsalen, miconazole, MONISTAT-DERM, MONISTAT 7, MOTRIN, MYSOLINE, nelfinavir, NEORAL, nifedipine, NORPACE, NORVIR, omeprazole, oral contraceptives, OXSORALEN, oxcarbazepine, PLAVIX, PRIFTIN, PRILOSEC, primidone, PROCARDIA, PROCARDIA XL, PROGLYCEM, PROLOPRIM, PROZAC, quetiapine, QUINAGLUTE DURA-TABS, QUINIDEX, quinidine, RESCRIPTOR, RIFADIN, rifampin, RIMACTANE, rifapentine, ritonavir, SANDIMMUNE, saquinavir, SEROQUEL, sertindole, SLO-BID, sucralfate, sulfamethizole, sulfamethoxazole, TAGAMET, THEO-24, theophylline, THIOSULFIL, tiagabine, ticlodipine, TICLID, TOPAMAX, topiramate, TORADOL, TRILEPTAL, trimethoprim, TRIMPEX, valproic acid, VELBAN, VIBRAMYCIN, vinblastine, VIRACEPT, vitamin D, ZYLOPRIM.

Adverse Effects [top]

Call your doctor immediately if you experience:

  • appetite and weight loss
  • painful, tingling, or numb hands or feet
  • bleeding, tender, or enlarged gums
  • difficulty breathing
  • chills
  • clumsiness or unsteadiness
  • chest discomfort
  • confusion
  • dark urine
  • defects in intelligence, short-term memory, learning ability, or attention
  • dizziness
  • fever
  • hand trembling
  • headache
  • joint pain
  • light gray stools
  • muscle pain
  • nausea or vomiting
  • nosebleeds or other unusual bleeding or bruising
  • restlessness or agitation
  • severe stomach pain
  • skin rash or itching
  • slurred speech or stuttering
  • sore throat
  • uncontrolled movements of eyes, hands, arms, legs, lips, tongue, or cheeks
  • unusual excitement, nervousness, or irritability
  • unusual tiredness or weakness
  • yellow eyes or skin
  • penile pain
  • bone disorders or fractures

Call your doctor if these symptoms continue:

  • constipation
  • mild dizziness
  • mild drowsiness
  • nausea and vomiting
  • enlargement of facial features
  • swelling of breasts in males
  • headache
  • unusual and excessive hair growth on body and face
  • trouble sleeping
  • muscle twitching

Signs of overdose:

  • clumsiness or unsteadiness
  • staggering walk
  • blurred or double vision
  • severe confusion
  • severe dizziness or drowsiness
  • stuttering
  • slurred speech
  • blood pressure changes
  • nausea and vomiting
  • continuous, uncontrolled back-and-forth and/or rolling eye movements
  • seizures
  • tremor
  • unusual tiredness or weakness

If you suspect an overdose, call this number to contact your poison control center: (800) 222-1222.

Periodic Tests[top]

Ask your doctor which of these tests should be done periodically while you are taking this drug:

  • blood levels of phenytoin
  • electroencephalogram (EEG)
  • complete blood and platelet count
  • thyroid function tests
  • dental exam, every three months
  • liver function tests
  • blood levels of calcium
  • blood levels of albumin
  • respiratory function tests
  • blood pressure
  • blood levels of folate
  • blood levels of phosphate
  • cardiac function tests
  • physical exam

last reviewed December 31, 2022