What is the most important information I should know about phenytoin?
You should not use phenytoin if you also take delavirdine (Rescriptor).
What is phenytoin?
Phenytoin is an anticonvulsant medication that is used to control seizures. Phenytoin does not treat all types of seizures, and your doctor will determine if it is the right medicine for you.
Phenytoin may also be used for purposes not listed in this medication guide.
What should I discuss with my healthcare provider before taking phenytoin?
You should not use phenytoin if you are allergic to it, or if you have ever had:
- liver problems caused by phenytoin;
- an allergy to similar medicines such as ethotoin, fosphenytoin, or mephenytoin; or
- if you currently take delavirdine (Rescriptor).
Tell your doctor if you have ever had:
- heart problems;
- liver disease;
- diabetes;
- depression;
- suicidal thoughts or actions;
- 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 are of Asian ancestry (you may need a special blood test to determine your risk for having a skin reaction to phenytoin).
Some people have thoughts about suicide while taking phenytoin. Your doctor will need to check your progress at regular visits. Your family or other caregivers should also be alert to changes in your mood or symptoms.
Seizure control is very important during pregnancy. Do not start or stop taking this medicine without your doctor's advice if you are pregnant. Phenytoin may harm an unborn baby, but having a seizure during pregnancy could harm both mother and baby. Tell your doctor right away if you become pregnant while taking this medicine.
If you are pregnant, your name may be listed on a pregnancy registry to track the effects of phenytoin on the baby.
If you have taken phenytoin during pregnancy, be sure to tell the doctor who delivers your baby about your phenytoin use. Both you and the baby may need to receive medications to prevent excessive bleeding during delivery and just after birth.
Phenytoin can make birth control pills less effective. Ask your doctor about using a non-hormonal birth control (condom, diaphragm with spermicide) to prevent pregnancy.
It may not be safe to breastfeed while using this medicine. Ask your doctor about any risk.
How should I take phenytoin?
Follow all directions on your prescription label and read all medication guides or instruction sheets. Your doctor may occasionally change your dose. Use the medicine exactly as directed.
Swallow an extended-release capsule whole and do not crush, chew, break, or open it.
Phenytoin chewable tablets are not for once-per-day dosing. You must take them 2 or 3 times per day. Follow your doctor's dosing instructions very carefully.
Shake the oral suspension (liquid) before you measure a dose. Use the dosing syringe provided, or use a medicine dose-measuring device (not a kitchen spoon).
You may need frequent blood tests. You may also need a blood test when switching from one form of phenytoin to another. Visit your doctor regularly.
Tell your doctor if phenytoin does not seem to work as well in controlling your seizures. Do not stop using phenytoin suddenly, even if you feel fine. Stopping suddenly may cause increased seizures. Follow your doctor's instructions about tapering your dose.
In case of emergency, wear or carry medical identification to let others know you have seizures.
Phenytoin can cause swelling in your gums. Brush and floss your teeth and visit your dentist regularly to help prevent this problem.
Store at room temperature away from moisture, light, and heat.
What happens if I miss a dose?
Take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.
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 while taking phenytoin?
Avoid drinking alcohol while you are taking phenytoin. Alcohol use can increase your blood levels of phenytoin and may increase side effects. Daily alcohol use can decrease your blood levels of phenytoin, which can increase your risk of seizures.
Ask a doctor or pharmacist before using over-the-counter medicines such as cimetidine, omeprazole, St. John's wort, or vitamins and mineral supplements that contain folic acid.
Avoid driving or hazardous activity until you know how this medicine will affect you. Your reactions could be impaired.
Avoid taking antacids at the same time you take phenytoin. Antacids can make it harder for your body to absorb the medication.
What are the possible side effects of phenytoin?
Get emergency medical help if you have signs of an allergic reaction (hives, difficult breathing, swelling in your face or throat) or a severe skin reaction (fever, sore throat, burning in your eyes, skin pain, red or purple skin rash that spreads and causes blistering and peeling).
Seek medical treatment if you have a serious drug reaction that can affect many parts of your body. Symptoms may include: skin rash, fever, swollen glands, muscle aches, severe weakness, unusual bruising, or yellowing of your skin or eyes.
Report any new or worsening symptoms to your doctor, such as: mood or behavior changes, anxiety, panic attacks, trouble sleeping, or if you feel impulsive, irritable, agitated, hostile, aggressive, restless, hyperactive (mentally or physically), more depressed, or have thoughts about suicide or hurting yourself.
Call your doctor at once if you have:
- slow or uneven heartbeats, chest pain, fluttering in your chest, and dizziness (like you might pass out);
- any skin rash, no matter how mild;
- fever, chills, sore throat, swollen glands;
- red or swollen gums, mouth sores;
- easy bruising, unusual bleeding, purple or red spots under your skin; or
- liver problems --loss of appetite, upper stomach pain, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes).
Common side effects may include:
- drowsiness, confusion;
- slurred speech;
- abnormal eye movement; or
- problems with balance, coordination, or muscle movement.
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.
What other drugs will affect phenytoin?
Sometimes it is not safe to use certain medications at the same time. Some drugs can affect your blood levels of other drugs you take, which may increase side effects or make the medications less effective.
Many drugs can affect phenytoin. Not all possible interactions are listed here. TELL YOUR DOCTOR ABOUT ALL OTHER MEDICINES YOU USE, and any you start or stop using during treatment with phenytoin. This includes prescription and over-the-counter medicines, vitamins, and herbal products.
Where can I get more information?
Your pharmacist can provide more information about phenytoin.
