Home - National Multiple Sclerosis Society

Skip to navigation Skip to content
Treatments > Medications Used In MS

Brand Name Chemical Name

(U.S. and Canada)

Phenytoin (fen-i-toyn)

Primary Usage in MS

Generic Available
Pain (dyesthesias) Yes (U.S.)

Phenytoin is one of a group of hydantoin anticonvulsants that are used most commonly in the management of seizures in epilepsy. It is used in MS to manage painful dysesthesias (most commonly trigeminal neuralgia) caused by abnormalities in the sensory pathways in the brain and spinal cord.

This drug may interact with the effects of alcohol and other central nervous system depressants (e.g., antihistamines, sedatives, tranquilizers, certain prescription pain medications, seizure medications, muscle relaxants, sleeping medications). Be sure your physician knows if you are taking these or any other medications.

Oral contraceptives (birth control pills) that contain estrogen may not be as effective if taken in conjunction with phenytoin. Consult with your physician about using a different or additional form of birth control to avoid unplanned pregnancies.

This medication may affect the blood sugar levels of diabetic individuals. Check with your physician if you notice any change in the results of your blood or urine sugar level tests while taking phenytoin.

Antacids or medicines for diarrhea can reduce the effectiveness of phenytoin. Do not take any of these medications within two to three hours of the phenytoin.

Before having any type of dental treatment or surgery, be sure to inform your physician or dentist if you are taking phenytoin. Medications commonly used during surgical and dental treatments can increase the side effects of phenytoin.

There have been reports of increased birth defects when hydantoin anticonvulsants were used for seizure control during pregnancy. It is not definitely known whether these medications were the cause of the problem. Be sure to tell your physician if you are pregnant or considering becoming pregnant. Phenytoin passes into breast milk in small amounts.

Possible Side Effects
Side effects that may go away as your body adjusts to the medication and do not require medical attention unless they continue or are bothersome: constipation*; mild dizziness*; mild drowsiness*.

Side effects that should be reported to your physician: bleeding or enlarged gums; confusion; enlarged glands in the neck or underarms; mood or mental changes*; muscle weakness or pain*; skin rash or itching; slurred speech or stuttering; trembling; unusual nervousness or irritability.

Symptoms of overdose that require immediate attention: sudden blurred or double vision*; sudden severe clumsiness or unsteadiness*; sudden severe dizziness or drowsiness*; staggering walk*; severe confusion or disorientation.

*Since it may be difficult to distinguish between certain common symptoms of MS and some side effects of phenytoin, be sure to consult your health care professional if an abrupt change of this type occurs.

Medication Index

Other Medications Used to Treat MS-related Pain

About Pain in MS

Pain: The Basic Facts
Types of pain, therapies, self-help, resources, and more.

Reprinted with permission from Rosalind C. Kalb (ed.), Multiple Sclerosis: The Questions You Have—The Answers You Need, 3rd Edition. New York: Demos Medical Publishing, Inc., 2004

Last updated January 13, 2005