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Phenytoin for Epilepsy


Generic NameBrand Name
phenytoinDilantin, Phenytek

Fosphenytoin is a form of phenytoin that is given in a vein (intravenous, or IV) or into a muscle (intramuscular, or IM) and can be used in cases of status epilepticus.

How It Works

Phenytoin prevents seizures by reducing activity in certain areas of the brain.

Why It Is Used

Phenytoin can be used for:

Phenytoin should not be used to treat absence seizures or myoclonic seizures.

How Well It Works

Phenytoin helps to control partial seizures and generalized tonic-clonic seizures.1

Side Effects

Common side effects of phenytoin include:

  • Swollen, tender gums.
  • Growth of facial and body hair.
  • Enlarged or rough facial features.
  • Acne.

High levels of phenytoin in the body may also cause:

  • Drowsiness.
  • Double vision.
  • Dizziness.
  • Tremors or shaking.
  • Decreased coordination.
  • Confusion and inability to concentrate.

In rare cases, phenytoin may cause a serious skin rash. Contact your doctor if you develop a rash while taking phenytoin.

Using phenytoin for a long time can increase your risk for osteoporosis and broken bones.

FDA Advisory. The U.S. Food and Drug Administration (FDA) has issued an advisory on antiepileptic drugs (AEDs) and the risk of suicide. Talk to your doctor about these possible side effects and the warning signs of suicide in adults and in children and teens.

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

What To Think About

It may take time and careful, controlled adjustments by you and your doctor to find the combination, schedule, and dosing of medicine to best manage your epilepsy. The goal is to prevent seizures while causing as few side effects as possible. After you and your doctor figure out the medicine program that works best for you, make sure to follow your program exactly as prescribed.

  • Adverse effects. Phenytoin has side effects that may affect your appearance (excess hair, acne, enlarged or rough facial features). Many people may be unwilling to deal with these side effects. Most people tolerate the drug fairly well. But at high levels it can affect your thinking (cognitive impairment). Because it can cause osteoporosis, phenytoin often is not the best choice for older adults. In rare cases, phenytoin can affect blood counts, the liver, or the kidneys.
  • Drug interactions. Many medicines for epilepsy can interact with other medicines you may be taking. This means that your epilepsy medicine may not work as well, or it may affect the way another medicine you are taking works. Some of these interactions can be dangerous. Make sure to tell your doctor about all the medicines, herbal pills, and dietary supplements you are taking. Phenytoin may reduce the effectiveness of birth control pills. A woman taking phenytoin may need to use a method of birth control other than birth control pills to reduce her chances of becoming pregnant.
  • Risk of birth defects. All medicines for epilepsy have some risk of birth defects. But the risk of birth defects needs to be carefully compared to other risks to the baby if the mother stops taking her epilepsy medicine. If you are thinking about becoming pregnant, be sure to plan ahead and talk with your doctor about the benefits and risks of taking epilepsy medicine during your pregnancy. It you are already pregnant, it is not too late. The best thing to do is talk to your doctor about your pregnancy before you make any changes to the medicines you are taking.
  • Other concerns. Getting regular blood tests to monitor the level of medicine in your blood can help keep your dose in the appropriate range. For some people, phenytoin may cause side effects or carry risks that are not yet fully known. Report any unexpected side effects or problems to your doctor.

Complete the new medication information form (PDF) (What is a PDF document?) to help you understand this medication.



  1. Drugs for epilepsy (2008). Treatment Guidelines From The Medical Letter, 6(70): 37–46.


By Healthwise Staff
John Pope, MD - Pediatrics
Steven C. Schachter, MD - Neurology
Last Revised August 28, 2013

Last Revised: August 28, 2013

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