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phenytoin

Pronunciation

Generic Name: phenytoin (oral) (FEN i toyn)
Brand Name: Dilantin, Phenytek, Dilantin-125, Dilantin Infatabs, 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 does not treat all types of seizures, and your doctor will determine if it is the right medicine for you.

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

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

You should not use phenytoin if you also take delavirdine (Rescriptor).

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

You should not use phenytoin if you also take delavirdine (Rescriptor), or if you are allergic to phenytoin or similar medicines such as ethotoin, fosphenytoin, or mephenytoin.

To make sure phenytoin is safe for you, tell your doctor if you have:

  • liver disease;

  • 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); or

  • if you drink large amounts of alcohol.

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 phenytoin. 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 this medicine 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.

If you become pregnant while taking phenytoin, your name may be listed on a pregnancy registry. This is to track the outcome of the pregnancy and to evaluate any effects of phenytoin on the baby.

Phenytoin can make birth control pills less effective. Ask your doctor about using non hormonal birth control (condom, diaphragm with spermicide) to prevent pregnancy while taking phenytoin.

Phenytoin can pass into breast milk and may harm a nursing baby. You should not breast-feed while you are using phenytoin.

How should I take phenytoin?

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 phenytoin capsule that has changed colors. Call your doctor for a new prescription.

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 phenytoin, 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 phenytoin to treat seizures, do not stop using phenytoin 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 phenytoin. Any medical care provider who treats you should know that you take seizure medication.

Store at room temperature away from moisture, light, and heat.

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. Overdose symptoms may include twitching eye movements, slurred speech, loss of balance, tremor, muscle stiffness or weakness, nausea, vomiting, feeling light-headed, fainting, and slow or shallow breathing.

What should I avoid while taking phenytoin?

Avoid drinking alcohol while you are taking phenytoin. Alcohol use can increase your blood levels of phenytoin and may increase side effects. Daily alcohol use can decrease your blood levels of phenytoin, which can increase your risk of seizures.

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 signs of an allergic reaction: 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.

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; or

  • severe skin reaction--fever, sore throat, swelling in your face or tongue, burning in your eyes, skin pain, followed by a red or purple skin rash that spreads (especially in the face or upper body) and causes blistering and peeling.

Common side effects may include:

  • nausea, vomiting, constipation;

  • tremors, slurred speech, loss of balance or coordination;

  • rash;

  • headache;

  • confusion, dizziness, nervousness; or

  • sleep problems (insomnia).

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.

See also: Side effects (in more detail)

Phenytoin dosing information

Usual Adult Dose for Seizures:

EXTENDED RELEASE FORMULATION (100 mg per capsule):
-DIVIDED DAILY DOSAGE:
Initial dose (in patients not previously treated with this drug): 1 capsule orally 3 times a day; dosage then adjusted to suit individual requirements
Maintenance dose: For most adults the satisfactory maintenance dosage will be 1 capsule 3 to 4 times a day; for others an increase up to 2 capsules 3 times a day may be made, if necessary
-ONCE-A-DAY DOSAGE:
If seizure control is established with divided doses of 3 capsules orally daily, then 300 mg orally once a day may be considered
-LOADING DOSE:
Some clinicians use an oral loading dose in adults who require rapid steady-state serum levels and where IV administration is not desirable. This dosing regimen should be reserved for patients in a clinic or hospital setting where phenytoin serum levels can be closely monitored. Patients with a history of renal or liver disease should not receive the oral loading regimen: Initially, 1 gm is divided into 3 doses (400 mg, 300 mg, 300 mg) and administered at 2 hour intervals. Normal maintenance dosage is then instituted 24 hours after the loading dose, with frequent serum level determinations.

CHEWABLE TABLETS (50 mg per tablet):
Initial dose (in patients not previously treated with this drug): 2 tablets chewed 3 times a day; dosage then adjusted to suit individual requirements; for most adults, the satisfactory maintenance dosage will be 6 to 8 tablets daily; an increase to 12 tablets daily may be made, if necessary

SUSPENSION (125 mg per 5 mL):
Initial dose (in patients not previously treated with this drug): 5 mL orally 3 times daily; dosage then adjusted to suit individual requirements; an increase to 25 mL orally daily may be made, if necessary

Use: For the control of tonic-clonic (grand mal) and psychomotor (temporal lobe) seizures

Usual Adult Dose for Status Epilepticus:

IV: Treatment can be initiated either with a loading dose or an infusion:
-LOADING DOSE: 10 to 15 mg/kg by slow IV infusion, not exceeding 50 mg/min; infusion must be completed within 1 to 4 hours
IV/ORAL:
Maximum rate: 50 mg/min
-NONEMERGENT LOADING AND MAINTENANCE DOSING: Because of the risks of cardiac and local toxicity associated with IV administration, oral dosing should be used whenever possible:
LOADING DOSE: 10 to 15 mg/kg IV (not to exceed 50 mg/min in adults)
MAINTENANCE DOSE: The loading dose should be followed by maintenance doses by oral or IV administration every 6 to 8 hours
-IM: Ordinarily, this drug should not be given IM because of the risk of necrosis, abscess formation, and erratic absorption. If IM administration is required, compensating dosage adjustments are necessary to maintain therapeutic plasma levels. An IM dose 50% greater than the oral dose is necessary to maintain these levels. When returned to oral administration, the dose should be reduced by 50% of the original oral dose for 1 week to prevent excessive plasma levels due to sustained release from IM tissue sites.

Comments:
-Electrocardiogram and blood pressure should be monitored continuously.
-The patient should be observed for signs of respiratory depression.
-Phenytoin plasma levels should be obtained in the management of status epilepticus and in the subsequent establishment of maintenance dosage.
-Other measures, including concomitant administration of an IV benzodiazepine such as diazepam, or an IV short-acting barbiturate, will usually be necessary for rapid control of seizures because of the required slow rate of administration of phenytoin.
-If IV administration does not terminate seizures, the use of other anticonvulsants, IV barbiturates, general anesthesia and other appropriate measures should be considered.
-IM administration should not be used in the treatment of status epilepticus because the attainment of peak plasma levels may require up to 24 hours.

Use: For the control of generalized tonic-clonic status epilepticus

Usual Adult Dose for Seizure Prophylaxis During or Following Neurosurgery:

-ORAL:
Initial dose: 5 mg/kg/day orally in 2 or 3 equally divided doses, with subsequent dosage individualized to a maximum of 300 mg orally daily
-Maintenance dose: 4 to 8 mg/kg. Children over 6 years old and adolescents may require the minimum adult dose (300 mg/day)

-IV:
Loading dose: Do not exceed an infusion rate of 1 to 3 mg/kg/min (or 50 mg per minute, whichever is slower) in pediatric patients

Comments:
-Because of the increased risk of adverse cardiovascular reactions associated with rapid IV administration, the rate should not exceed 1 to 3 mg/kg/min or 50 mg per minute in children, whichever is slower.

Use: For the prevention and treatment of seizures occurring during or following neurosurgery

Usual Pediatric Dose for Seizures:

-ORAL:
Initial dose: 5 mg/kg/day orally in 2 or 3 equally divided doses, with subsequent dosage individualized to a maximum of 300 mg orally daily
-Maintenance dose: 4 to 8 mg/kg. Children over 6 years old and adolescents may require the minimum adult dose (300 mg/day)

Use: For the control of tonic-clonic (grand mal) and psychomotor (temporal lobe) seizures

Usual Pediatric Dose for Status Epilepticus:

-IV:
-EMERGENT LOADING DOSE: 15 to 20 mg/kg by slow IV infusion (to produce plasma concentrations of phenytoin within the generally accepted therapeutic range of 10 to 20 mcg/mL); infusion must be completed within 1 to 4 hours
Maximum rate: 1 to 3 mg/kg/min or 50 mg/min, whichever is slower
Maintenance rate: 100 mg orally or IV every 6 to 8 hours
-NONEMERGENT LOADING AND MAINTENANCE DOSING: Because of the risks of cardiac and local toxicity associated with IV administration, oral dosing should be used whenever possible:
LOADING DOSE: 1 to 3 mg/kg/min (or 50 mg/min, whichever is slower)
MAINTENANCE DOSE: The loading dose should be followed by maintenance doses by oral or IV administration every 6 to 8 hours
-IM: Ordinarily, this drug should not be given IM because of the risk of necrosis, abscess formation, and erratic absorption. If IM administration is required, compensating dosage adjustments are necessary to maintain therapeutic plasma levels. An IM dose 50% greater than the oral dose is necessary to maintain these levels. When returned to oral administration, the dose should be reduced by 50% of the original oral dose for 1 week to prevent excessive plasma levels due to sustained release from IM tissue sites.

Comments:
-Electrocardiogram and blood pressure should be monitored continuously.
-The patient should be observed for signs of respiratory depression.
-Phenytoin plasma levels should be obtained in the management of status epilepticus and in the subsequent establishment of maintenance dosage.
-Other measures, including concomitant administration of an IV benzodiazepine such as diazepam, or an IV short-acting barbiturate, will usually be necessary for rapid control of seizures because of the required slow rate of administration of phenytoin.
-If IV administration does not terminate seizures, the use of other anticonvulsants, IV barbiturates, general anesthesia and other appropriate measures should be considered.
-IM administration should not be used in the treatment of status epilepticus because the attainment of peak plasma levels may require up to 24 hours.

Use: For the control of generalized tonic-clonic status epilepticus

Usual Pediatric Dose for Seizure Prophylaxis During or Following Neurosurgery:

-ORAL:
Initial dose: 5 mg/kg/day orally in 2 or 3 equally divided doses, with subsequent dosage individualized to a maximum of 300 mg orally daily
-Maintenance dose: 4 to 8 mg/kg. Children over 6 years old and adolescents may require the minimum adult dose (300 mg/day)

-IV:
Loading dose: Do not exceed an infusion rate of 1 to 3 mg/kg/min (or 50 mg per minute, whichever is slower) in pediatric patients

Comments:
-Because of the increased risk of adverse cardiovascular reactions associated with rapid IV administration, the rate should not exceed 1 to 3 mg/kg/min or 50 mg per minute in children, whichever is slower.

Use: For the prevention and treatment of seizures occurring during or following neurosurgery

What other drugs will affect phenytoin?

Sometimes it is not safe to use certain medications at the same time. Some drugs can raise or lower your blood levels of phenytoin, which may cause side effects or make phenytoin less effective. Phenytoin can also affect blood levels of certain other drugs, making them less effective or increasing side effects.

Taking phenytoin with other drugs that make you sleepy or slow your breathing can increase these effects. Ask your doctor before taking phenytoin with a sleeping pill, narcotic pain medicine, muscle relaxer, or medicine for anxiety, depression, or seizures.

Many drugs can interact with phenytoin. Not all possible interactions are listed here. TELL YOUR DOCTOR ABOUT ALL OTHER MEDICINES YOU USE, and any you start or stop using during treatment with phenytoin. This includes prescription and over-the-counter medicines, vitamins, and herbal products.

Where can I get more information?

  • Your pharmacist can provide more information about phenytoin.
  • Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.
  • Disclaimer: Every effort has been made to ensure that the information provided by Cerner Multum, Inc. ('Multum') is accurate, up-to-date, and complete, but no guarantee is made to that effect. Drug information contained herein may be time sensitive. Multum information has been compiled for use by healthcare practitioners and consumers in the United States and therefore Multum does not warrant that uses outside of the United States are appropriate, unless specifically indicated otherwise. Multum's drug information does not endorse drugs, diagnose patients or recommend therapy. Multum's drug information is an informational resource designed to assist licensed healthcare practitioners in caring for their patients and/or to serve consumers viewing this service as a supplement to, and not a substitute for, the expertise, skill, knowledge and judgment of healthcare practitioners. The absence of a warning for a given drug or drug combination in no way should be construed to indicate that the drug or drug combination is safe, effective or appropriate for any given patient. Multum does not assume any responsibility for any aspect of healthcare administered with the aid of information Multum provides. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the drugs you are taking, check with your doctor, nurse or pharmacist.

Copyright 1996-2012 Cerner Multum, Inc. Version: 13.02. Revision Date: 2015-10-14, 3:26:27 PM.

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