Phenytoin should not be used to treat absence seizures or
How Well It Works
Phenytoin helps to control partial seizures and generalized tonic-clonic seizures.1
Common side effects of phenytoin
Swollen, tender gums.
facial and body hair.
Enlarged or rough facial
High levels of phenytoin in the body may also cause:
inability to concentrate.
In rare cases, phenytoin may cause a serious skin rash. Contact your doctor if you develop a rash while taking
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.
Drugs for epilepsy (2008). Treatment Guidelines From The Medical Letter, 6(70): 37–46.
How this information was developed to help you make better health decisions.