phenytoin

Generic Name: phenytoin (oral) (FEN i toyn)

Brand names: Dilantin, Dilantin Infatabs, Dilantin-125, Phenytek, Dilantin Kapseals, Phenytoin Sodium, Prompt, Di-Phen

What is phenytoin?

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

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

Phenytoin may also be used for other purposes not listed in this medication guide.

What is the most important information I should know about phenytoin?

You may have thoughts about suicide while taking this medication. Your doctor will need to check you at regular visits. Do not miss any scheduled appointments.

Call your doctor at once if you have any new or worsening symptoms such as: mood or behavior changes, depression, anxiety, or if you feel agitated, hostile, restless, hyperactive (mentally or physically), or have thoughts about suicide or hurting yourself.

What should I discuss with my healthcare provider before taking phenytoin?

You may have thoughts about suicide while taking this medication. Tell your doctor if you have new or worsening depression or suicidal thoughts during the first several months of treatment, or whenever your dose is changed.

Your family or other caregivers should also be alert to changes in your mood or symptoms. Your doctor will need to check you at regular visits. Do not miss any scheduled appointments.

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.

How should I take phenytoin?

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

Do not crush, chew, break, or open an extended-release capsule. Swallow it whole. Breaking or opening the pill may cause too much of the drug to be released at one time. Shake the oral suspension (liquid) well just before you measure a dose. Measure the liquid with a special dose-measuring spoon or medicine cup, not with a regular table spoon. If you do not have a dose-measuring device, ask your pharmacist for one.

To be sure this medication is helping your condition, your blood may need to be tested often. You may also need a blood test when switching from one form of phenytoin to another. Visit your doctor regularly.

If you are taking phenytoin to treat seizures, keep taking the medication even if you feel fine. You may have an increase in seizures if you stop taking phenytoin. Follow your doctor's instructions. Wear a medical alert tag or carry an ID card stating that you take phenytoin. Any medical care provider who treats you should know that you are taking a seizure medication. Store at room temperature away from moisture, light, and heat.

See also: Phenytoin dosage (in more detail)

What happens if I miss a dose?

Take the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222. An overdose of phenytoin can be fatal.

What should I avoid while taking phenytoin?

Drinking alcohol can increase some of the side effects of phenytoin, and can also increase your risk of seizure.

Avoid taking antacids at the same time you take phenytoin. Antacids can make it harder for your body to absorb the medication.

Phenytoin may impair your thinking or reactions. Be careful if you drive or do anything that requires you to be alert.

Phenytoin side effects

Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Less serious side effects may include:

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  headache, joint pain.

  
  

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Phenytoin Dosing Information

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.

Suspension: 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.

IV: 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.

IM: 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:

IV:
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.

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

What other drugs will affect phenytoin?

Drugs that can increase phenytoin levels in your blood include:

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  stomach acid reducers such as cimetidine (Tagamet), ranitidine (Zantac), famotidine (Pepcid), or nizatidine (Axid);

  
  


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  certain sedatives (such as Librium or Valium) or antidepressants (such as Prozac);

  
  


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  estrogen hormone replacement;

  
  

This list is not complete and there are many other medicines that can interact with phenytoin. Tell your doctor about all medications you use. This includes prescription, over-the-counter, vitamin, and herbal products. Do not start a new medication without telling your doctor. Keep a list of all your medicines and show it to any healthcare provider who treats you.

More phenytoin resources

• Phenytoin Side Effects (in more detail)
• Phenytoin Dosage
• Phenytoin Use in Pregnancy & Breastfeeding
• Drug Images
• Phenytoin Drug Interactions
• Phenytoin Support Group
• 46 Reviews for Phenytoin - Add your own review/rating

• phenytoin Advanced Consumer (Micromedex) - Includes Dosage Information


• Phenytoin Professional Patient Advice (Wolters Kluwer)


• Phenytoin MedFacts Consumer Leaflet (Wolters Kluwer)


• Phenytoin Monograph (AHFS DI)


• Dilantin Suspension MedFacts Consumer Leaflet (Wolters Kluwer)


• Dilantin Consumer Overview


• Dilantin Prescribing Information (FDA)


• Dilantin Infatabs Chewable Tablets MedFacts Consumer Leaflet (Wolters Kluwer)


• Dilantin Infatabs Prescribing Information (FDA)


• Dilantin Kapseals Extended-Release Capsules MedFacts Consumer Leaflet (Wolters Kluwer)


• Dilantin Kapseals Prescribing Information (FDA)


• Dilantin-125 Prescribing Information (FDA)


• Phenytek Prescribing Information (FDA)

Compare phenytoin with other medications

• Anxiety
• Arrhythmia
• Epilepsy
• Neurosurgery
• Peripheral Neuropathy
• Rheumatoid Arthritis
• Seizures
• Status Epilepticus
• Trigeminal Neuralgia

Where can I get more information?

• Your pharmacist can provide more information about phenytoin.

See also: phenytoin side effects (in more detail)