Phenytoin for Epilepsy

Browse By All Topics


Phenytoin for Epilepsy


Generic NameBrand Name
phenytoinDilantin, Phenytek

Phenytoin is available in liquid, capsule, and chewable tablet forms. It is also available as an injection (shot).

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 is one of the drugs of choice 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.
  • Skin rash.

High levels of phenytoin in the body may also cause:

  • Drowsiness.
  • Double vision.
  • Dizziness.
  • Tremors or shaking.
  • Decreased coordination.
  • Confusion and inability to concentrate.
  • Osteoporosis (when taken for months to years).

The U.S. Food and Drug Administration (FDA) has issued a warning on antiepileptic medicines and the risk of suicide and suicidal thoughts. The FDA does not recommend that people stop using these medicines. Instead, people who take antiepileptic medicine should be watched closely for warning signs of suicide. People who take antiepileptic medicine and who are worried about this side effect should talk to a doctor.

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.
  • 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.


ByHealthwise Staff
Primary Medical ReviewerSusan C. Kim, MD - Pediatrics
Specialist Medical ReviewerSteven C. Schachter, MD - Neurology
Last RevisedAugust 26, 2011

Last Revised: August 26, 2011

This information does not replace the advice of a doctor. Healthwise, Incorporated disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use.

How this information was developed to help you make better health decisions.

© 1995-2012 Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated.