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. It does not treat all types of seizures, and your doctor will determine if it is the right medication for you.
Phenytoin may also be used for purposes not listed in this medication guide.
You should not use phenytoin if you also take delavirdine (Rescriptor), or if you are allergic to phenytoin, ethotoin (Peganone), fosphenytoin (Cerebyx), or mephenytoin (Mesantoin). If you are pregnant, DO NOT START TAKING phenytoin unless your doctor tells you to. Phenytoin may cause harm to an unborn baby, but having a seizure during pregnancy could harm both the mother and the baby. If you become pregnant while taking phenytoin, DO NOT STOP TAKING the medicine without your doctor's advice. Seizure control is very important during pregnancy and the benefits of preventing seizures may outweigh any risks posed by using phenytoin.
You may have thoughts about suicide while taking phenytoin. Your doctor will need to check you at regular visits. Do not miss any scheduled appointments.
Report any new or worsening symptoms to your doctor, 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.
Before taking this medicine
You should not use phenytoin if you also take delavirdine (Rescriptor), or if you are allergic to phenytoin, ethotoin (Peganone), fosphenytoin (Cerebyx), or mephenytoin (Mesantoin).
To make sure you can safely take phenytoin, tell your doctor if you have any of these other conditions:
- liver disease;
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.
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.
You may have thoughts about suicide while taking phenytoin. 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.
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.
FDA pregnancy category D. Phenytoin may cause harm to an unborn baby, but having a seizure during pregnancy could harm both the mother and the baby. If you are pregnant, DO NOT START TAKING phenytoin unless your doctor tells you to. If you become pregnant while taking phenytoin, DO NOT STOP TAKING the medicine without your doctor's advice.
See also: Pregnancy and breastfeeding warnings (in more detail)
Seizure control is very important during pregnancy. The benefit of preventing seizures may outweigh any risks posed by taking phenytoin. Follow your doctor's instructions about taking phenytoin while you are pregnant. Phenytoin can make birth control pills less effective. To prevent pregnancy while you are taking this medicine, use a non-hormonal form of birth control (such as a condom or diaphragm with spermicide). Phenytoin can pass into breast milk and may harm a nursing baby. You should not breast-feed while you are using this medicine.
How should I take phenytoin?
Take phenytoin 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. 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 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 phenytoin 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. Do not change your dose of phenytoin without your doctor's advice. Tell your doctor if the medication 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 are taking a seizure medication.
Store phenytoin 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?
Avoid drinking alcohol while you are taking phenytoin. Alcohol use can increase your blood levels of this medicine 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 any of these signs of an allergic reaction to phenytoin: 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, depression, anxiety, or if you feel agitated, hostile, restless, hyperactive (mentally or physically), or have thoughts about suicide or hurting yourself.
Call your doctor at once if you have a serious side effect while taking phenytoin such as:
fever, swollen glands, body aches, flu symptoms;
skin rash, easy bruising or bleeding, severe tingling, numbness, pain, muscle weakness;
upper stomach pain, loss of appetite, dark urine, jaundice (yellowing of the skin or eyes);
chest pain, irregular heart rhythm, feeling short of breath;
confusion, nausea and vomiting, swelling, rapid weight gain, urinating less than usual or not at all;
new or worsening cough with fever, trouble breathing;
tremor (uncontrolled shaking), restless muscle movements in your eyes, tongue, jaw, or neck;
patchy skin color, red spots, or a butterfly shaped skin rash over your cheeks and nose (worsens in sunlight); 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.
Less serious phenytoin side effects may include:
slurred speech, loss of balance or coordination;
swollen or tender gums; or
headache, 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 Phenytoin 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 of Phenytoin for Arrhythmias:
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
300 to 400 mg/day orally in divided doses 1 to 4 times a day
Usual Adult Dose of Phenytoin 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 of Phenytoin 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 of Phenytoin 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 of Phenytoin 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?
Many drugs can interact with phenytoin. Below is just a partial list. Tell your doctor if you are using:
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); or
theophylline (Elixophyllin, Theo-Dur, Theo-Bid, Theolair, Uniphyl).
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 about phenytoin
- Phenytoin chewable tablets
- Phenytoin extended-release capsules
- Phenytoin immediate-release capsules
- Phenytoin suspension
- More (2) »
Related treatment guides
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 phenytoin only for the indication prescribed.
Disclaimer: Every effort has been made to ensure that the information provided is accurate, up-to-date, and complete, but no guarantee is made to that effect. Drug information contained herein may be time sensitive. 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. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects.
Copyright 1996-2014 Cerner Multum, Inc. Version: 12.01. Revision Date: 2012-2-14, 5:04:25 PM.