By Medically reviewed by hellodoktor

Generic Name: Dilantin Brand Name(s): Generics only. No brands available.


What is Dilantin® (phenytoin) used for?

Dilantin® is an anti-epileptic drug, also called an anticonvulsant. It works by slowing down impulses in the brain that cause seizures.

Dilantin® is used to control seizures. Phenytoin does not treat all types of seizures, and your doctor will determine if it is the right medicine for you.

Dilantin® may also be used for purposes not listed in this medication guide.

How should I take Dilantin® (phenytoin)?

Take Dilantin® exactly as prescribed by your doctor. Follow all directions on your prescription label. Do not take this medicine in larger or smaller amounts or for longer than recommended.

Do not crush, chew, break, or open an extended-release capsule. Swallow it whole. Do not use any Dilantin® capsule that has changed colors. Call your doctor for a new prescription.

The chewable tablet must be chewed before you swallow it.

Shake the oral suspension (liquid) well just before you measure a dose. Measure liquid medicine with the dosing syringe provided, or with a special dose-measuring spoon or medicine cup. If you do not have a dose-measuring device, ask your pharmacist for one.

While using Dilantin®, you may need frequent blood tests. You may also need a blood test when switching from one form of phenytoin to another. Visit your doctor regularly.

If you are taking Dilantin® to treat seizures, do not stop using it suddenly, even if you feel fine. Stopping suddenly may cause increased seizures. Follow your doctor’s instructions about tapering your dose.

Tell your doctor if this medicine does not seem to work as well in treating your condition.

Wear a medical alert tag or carry an ID card stating that you take Dilantin®. Any medical care provider who treats you should know that you take seizure medication.

Phenytoin can cause swelling in your gums. Brush and floss your teeth and visit your dentist regularly to help prevent this problem.

How do I store Dilantin® (phenytoin)?

Dilantin® is best stored at room temperature away from direct light and moisture. To prevent drug damage, you should not store Dilantin® in the bathroom or the freezer. There may be different brands of Dilantin® that may have different storage needs. It is important to always check the product package for instructions on storage, or ask your pharmacist. For safety, you should keep all medicines away from children and pets.

You should not flush Dilantin® down the toilet or pour them into a drain unless instructed to do so. It is important to properly discard this product when it is expired or no longer needed. Consult your pharmacist for more details about how to safely discard your product.

Precautions & warnings

What should I know before using Dilantin® (phenytoin)?

Before using this drug, tell your doctor if:

  • You are pregnant or breastfeeding. This is because, while you are expecting or feeding a baby, you should only take medicines on the recommendation of a doctor.
  • You are taking any other medicines. This includes any medicines you are taking which are available to buy without a prescription, such as herbal and complementary medicines.
  • You have allergy with any of active or inactive ingredients of Dilantin® or other medications.
  • You have any other illnesses, disorders, or medical conditions.

You should not use Dilantin® if you are allergic to phenytoin or similar medicines such as ethotoin (Peganone), fosphenytoin (Cerebyx), or mephenytoin (Mesantoin), or if you have:

  • A history of liver problems caused by phenytoin
  • A heart condition called 2nd or 3rd degree “AV block”
  • A history of slow heart beats that have caused you to faint
  • A condition for which you also take delavirdine (Rescriptor)

You may have thoughts about suicide while taking this medicine. Your doctor will need to check your progress at regular visits while you are using Dilantin®. Your family or other caregivers should also be alert to changes in your mood or symptoms.

Patients of Asian ancestry may have a higher risk of developing a rare but serious skin reaction to phenytoin. Your doctor may recommend a blood test before you start the medication to determine your risk of this skin reaction.

Seizure control is very important during pregnancy. Do not start or stop taking Dilantin® without your doctor’s advice if you are pregnant. Phenytoin may cause harm to an unborn baby, but having a seizure during pregnancy could harm both mother and baby. Tell your doctor right away if you become pregnant while taking this medicine.

Is it safe during pregnancy or breastfeeding?

There are no adequate studies in women for determining risk when using Dilantin® during pregnancy or while breastfeeding. Please always consult with your doctor to weigh the potential benefits and risks before taking Dilantin®. Dilantin® is pregnancy risk category D, according to the US Food and Drug Administration (FDA).

FDA pregnancy risk category reference below:

  • A=No risk
  • B=No risk in some studies
  • C=There may be some risk
  • D=Positive evidence of risk
  • X=Contraindicated
  • N=Unknown

Side effects

What side effects can occur from Dilantin® (phenytoin)?

Get emergency medical help if you have any signs of an allergic reaction to Dilantin®: hives; difficulty breathing; swelling of your face, lips, tongue, or throat. You may be more likely to have an allergic reaction if you are African-American.

In rare cases, phenytoin may cause a severe drug reaction that can affect many parts of the body. This type of reaction can start several weeks after you begin using this medicine.

Seek medical treatment if you have new or worsening symptoms of fever, sore throat, mouth sores, facial swelling, a red or blistering skin rash, flu symptoms, swollen glands, feeling weak or tired, easy bruising, unusual bleeding, upper stomach pain, nausea, vomiting, loss of appetite, jaundice (yellowing of the skin or eyes), weight loss, pain or burning when you urinate, lower back pain, swelling in your legs or feet, cough, chest pain, or trouble breathing.

Report any new or worsening symptoms to your doctor, such as: mood or behavior changes, anxiety, panic attacks, trouble sleeping, or if you feel impulsive, irritable, agitated, hostile, aggressive, restless, hyperactive (mentally or physically), more depressed, or have thoughts about suicide or hurting yourself.

Call your doctor at once if you have:

  • Fever, swollen glands, sore throat, trouble breathing, painful mouth sores, sores around your eyes
  • Skin rash, easy bruising or bleeding, severe weakness
  • Severe muscle pain
  • Nausea, vomiting, upper stomach pain, loss of appetite, dark urine, jaundice (yellowing of the skin or eyes)
  • Bone pain (especially in your hips, legs, or lower back), trouble with walking
  • Severe skin reaction – fever, sore throat, swelling in your face or tongue, burning in your eyes, skin pain
  • Severe muscle pain

Common side effects may include:

  • Dizziness, drowsiness, confusion, nervousness
  • Tremors, slurred speech, loss of balance or coordination
  • Rash
  • Abnormal eye movement
  • Headache
  • Sleep problems (insomnia)

Not everyone experiences these side effects. There may be some side effects not listed above. If you have any concerns about a side-effect, please consult your doctor or pharmacist.


What drugs may interact with Dilantin® (phenytoin)?

Dilantin® may interact with other drugs that you are currently taking, which can change how your drug works or increase your risk for serious side effects. To avoid any potential drug interactions, you should keep a list of all the drugs you are using (including prescription drugs, nonprescription drugs, and herbal products) and share it with your doctor and pharmacist. For your safety, do not start, stop, or change the dosage of any drugs without your doctor’s approval.

Products that may interact with this drug are:

  • Antibiotics such as cycloserine (Seromycin), doxycycline (Doryx, Vibramycin, Adoxa), isoniazid (for treating tuberculosis), linezolid (Zyvox), rifampin (Rimactane, Rifadin, Rifamate), or sulfa drugs (Bactrim, Septra, Sulfatrim, SMX-TMP, and others)
  • An antidepressant (such as Elavil, Vanatrip, Limbitrol, Sinequan, Silenor, Pamelor, Paxil, Zoloft, Desyrel, and others)
  • Aspirin or other salicylates
  • Birth control pills or hormone replacement therapy
  • A blood thinner such as warfarin (Coumadin, Jantoven)
  • Certain sedatives (Librium, Librax, Limbitrol, Valium) or antidepressants (Desyrel, Luvox, Zoloft, Prozac, Rapiflux, Sarafem, Selfemra, Symbyax)
  • Heart medication such as amiodarone (Cordarone, Pacerone), digoxin (digitalis, Lanoxin), furosemide (Lasix), or quinidine (Quin-G)
  • Prochlorperazine (Compazine, Compro), promethazine (Pentazine, Phenergan, Anergan, Antinaus), and other phenothiazines
  • Steroid medicines (prednisone and others)
  • Seizure medicine (such as Carbatrol, Equetro, Tegretol, Solfoton, Depakene, or Depakote)
  • Stomach acid reducers (such Tagamet, Prilosec, Zegerid, Zantac, Pepcid, or Axid)
  • Theophylline (Elixophyllin, Theo-Dur, Theo-Bid, Theolair, Uniphyl)

Does food or alcohol interact with Dilantin® (phenytoin)?

Dilantin® may interact with food or alcohol by altering the way the drug works or increase the risk for serious side effects. Please discuss with your doctor or pharmacist any potential food or alcohol interactions before using this drug.

What health conditions may interact with Dilantin® (phenytoin)?

Dilantin® may interact with your health condition. This interaction may worsen your health condition or alter the way the drug works. It is important to always let your doctor and pharmacist know all the health conditions you currently have.

Health conditions that may interact with this drug are:

  • Liver disease
  • A history of abnormal heart rhythm found on an EKG (electrocardiograph)
  • Diabetes
  • A history of depression
  • A history of suicidal thoughts or actions
  • A vitamin D deficiency or any other condition that causes thinning of the bones
  • Porphyria (a genetic enzyme disorder that causes symptoms affecting the skin or nervous system)
  • If you drink large amounts of alcohol


The information provided is not a substitute for any medical advice. You should ALWAYS consult with your doctor or pharmacist before using Dilantin® (phenytoin).

What is the dose of Dilantin® (phenytoin) for an adult?

Usual Adult Dose for Seizures:

Oral (except suspension)

  • Loading dose: Only when indicated for inpatients.
  • 1 g orally divided in 3 doses (400 mg, 300 mg, 300 mg) given at 2 hour intervals. Then normal maintenance dosage started 24 hours after loading dose.
  • Initial dose: 100 mg extended release orally 3 times a day.
  • Maintenance dose: 100 mg orally 3 to 4 times a day. If seizure control is established with divided doses of three 100 mg capsules daily, once-a-day dosage with 300 mg of extended release phenytoin sodium may be considered. Alternatively, the dosage may need to be increased up to 200 mg orally 3 times a day, if necessary.


  • Patients who have received no previous treatment may be started on 125 mg (one teaspoonful) of the suspension three times daily, and the dose is then adjusted to suit individual requirements. An increase to five teaspoonfuls daily may be made, if necessary.


  • Do not exceed the infusion rate of 50 mg/min.
  • Loading dose: 10 to 15 mg/kg IV slowly.
  • Maintenance dose: 100 mg IV every 6 to 8 hours.


  • Avoid the IM route due to erratic absorption.

Usual Adult Dose for Arrhythmias:

Loading Dose: 1.25 mg/kg IV every 5 minutes. May repeat up to a loading dose of 15 mg/kg, or 250 mg orally 4 times a day for 1 day, then 250 mg twice daily for 2 days.

Maintenance Dose: 300 to 400 mg/day orally in divided doses 1 to 4 times a day.

Usual Adult Dose for Status Epilepticus:


Loading dose: Manufacturer recommends 10 to 15 mg/kg by slow IV administration (at a rate not exceeding 50 mg/minute). Alternatively, generally accepted guidelines suggest 15 to 20 mg/kg by slow IV administration (at a rate not exceeding 50 mg/minute).

Maintenance rate: 100 mg orally or IV every 6 to 8 hours

Maximum rate: 50 mg/minute

Maintenance dose: IV or Oral: 100 mg every 6 to 8 hours

Usual Adult Dose for Neurosurgery:

Neurosurgery (prophylactic): 100 to 200 mg IM at about 4 hour intervals during surgery and the immediate postoperative period. (Note: While the manufacturer recommends IM administration, this route may cause severe local tissue destruction and necrosis. Some clinicians recommend the use of fosphenytoin if IM administration is necessary.) If IM administration is not necessary, accepted protocol has been 100 to 200 mg IV at about 4 hour intervals during surgery and the immediate postoperative period.

What is the dose of Dilantin® (phenytoin) for a child?

Usual Pediatric Dose for Seizures:

Status Epilepticus: Loading Dose: Infants, Children: 15 to 20 mg/kg IV in a single or divided doses

Anticonvulsant: Loading Dose: All ages: 15 to 20 mg/kg orally (based on phenytoin serum concentrations and recent dosing history). The oral loading dose should be given in 3 divided doses administered every 2 to 4 hours.

Anticonvulsant: Maintenance Dose: (IV or oral) (Note: May initially divided daily dose into 3 doses/day, then adjust to suit individual requirements.)

Less than or equal to 4 weeks: Initial: 5 mg/kg/day in 2 divided doses

Usual: 5 to 8 mg/kg/day IV in 2 divided doses (may require dosing every 8 hours).

Greater than or equal to 4 weeks: Initial: 5 mg/kg/day in 2 to 3 divided doses

Usual: (may require up to every 8 hour dosing)

6 months to 3 years: 8 to 10 mg/kg/day

4 to 6 years: 7.5 to 9 mg/kg/day

7 to 9 years: 7 to 8 mg/kg/day

10 to 16 years: 6 to 7 mg/kg/day

Usual Pediatric Dose for Arrhythmias:

Greater than 1 year:

Loading Dose: 1.25 mg/kg IV every 5 minutes. May repeat up to a loading dose of 15 mg/kg.

Maintenance Dose: 5 to 10 mg/kg/day orally or IV in 2 to 3 divided doses

How is Dilantin® (phenytoin) available?

Dilantin® is available in the following dosage forms and strengths:

  • Capsule, extended release: phenytoin sodium 30mg

What should I do in case of an emergency or overdose?

In case of an emergency or an overdose, call your local emergency services or go to your nearest emergency room.

What should I do if I miss a dose?

If you miss a dose of Dilantin®, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and take your regular dose as scheduled. Do not take a double dose.

Hello Health Group does not provide medical advice, diagnosis or treatment.

Review Date: July 26, 2017 | Last Modified: September 13, 2019

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