Generic Name: phenytoin (FEN-i-toin)
Available Dosage Forms:
Therapeutic Class: Anticonvulsant
Chemical Class: Hydantoin (class)
Medically reviewed by Drugs.com. Last updated on Feb 11, 2021.
Uses for phenytoin
Phenytoin injection is used to control certain types of seizures (convulsions) in the treatment of epilepsy. It is also used to prevent and treat seizures that occur during brain surgery. Phenytoin is an anticonvulsant that works in the brain tissue to stop seizures.
Phenytoin is to be given only or under the direct supervision of a doctor.
Before using phenytoin
In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For phenytoin, the following should be considered:
Tell your doctor if you have ever had any unusual or allergic reaction to phenytoin or any other medicines. Also tell your health care professional if you have any other types of allergies, such as to foods, dyes, preservatives, or animals. For non-prescription products, read the label or package ingredients carefully.
Appropriate studies performed to date have not demonstrated pediatric-specific problems that would limit the usefulness of phenytoin injection in children.
Appropriate studies performed to date have not demonstrated geriatric-specific problems that would limit the usefulness of phenytoin injection in the elderly. However, elderly patients are more likely to have age-related liver, kidney, or heart problems, which may require an adjustment in the dose for patients receiving phenytoin injection.
There are no adequate studies in women for determining infant risk when using this medication during breastfeeding. Weigh the potential benefits against the potential risks before taking this medication while breastfeeding.
Interactions with medicines
Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are receiving phenytoin, it is especially important that your healthcare professional know if you are taking any of the medicines listed below. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.
Using phenytoin with any of the following medicines is not recommended. Your doctor may decide not to treat you with this medication or change some of the other medicines you take.
- Tenofovir Alafenamide
Using phenytoin with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.
- Abiraterone Acetate
- Dabigatran Etexilate
- Doxorubicin Hydrochloride Liposome
- Eslicarbazepine Acetate
- Ethinyl Estradiol
- Irinotecan Liposome
- St John's Wort
- Vincristine Sulfate Liposome
Using phenytoin with any of the following medicines may cause an increased risk of certain side effects, but using both drugs may be the best treatment for you. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.
- Aripiprazole Lauroxil
- Folic Acid
- Valproic Acid
Interactions with food/tobacco/alcohol
Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.
Using phenytoin with any of the following may cause an increased risk of certain side effects but may be unavoidable in some cases. If used together, your doctor may change the dose or how often you use phenytoin, or give you special instructions about the use of food, alcohol, or tobacco.
Other medical problems
The presence of other medical problems may affect the use of phenytoin. Make sure you tell your doctor if you have any other medical problems, especially:
- Blood or bone marrow problems (eg, agranulocytosis, leukopenia, thrombocytopenia) or
- Diabetes or
- Heart failure or
- Heart rhythm problems or
- Hypotension (low blood pressure) or
- Lymphadenopathy (lymph node problems) or
- Porphyria (an enzyme problem)—Use with caution. May make these conditions worse.
- Heart block (eg, Adams-Stokes syndrome, AV block, or sinoatrial block) or
- Sinus bradycardia (slow heartbeat)—Should not be used in patients with these conditions.
- Hypoalbuminemia (low albumin in the blood) or
- Kidney disease or
- Liver disease—Use with caution. The effects may be increased because of slower removal from the body.
Proper use of phenytoin
A nurse or other trained health professional will give you or your child phenytoin in a hospital. Phenytoin is given as a shot into a muscle or into a vein.
Your doctor will only give you or your child a few doses of phenytoin until your condition improves. You will be switched to an oral medicine that works the same way. If you have any concerns about this, talk to your doctor.
Precautions while using phenytoin
It is very important that your doctor check your progress closely while you or your child are receiving phenytoin. This is to see if it is working properly and to allow for a change in the dose. Blood tests may be needed to check for any unwanted effects.
Using phenytoin while you are pregnant can harm your unborn baby. Use an effective form of birth control to keep from getting pregnant. If you think you have become pregnant while using the medicine, tell your doctor right away.
Do not receive phenytoin while you or your child are also taking delavirdine (Rescriptor®). Using these medicines together may cause unwanted effects.
Phenytoin may cause some people to become dizzy, lightheaded, faint, or less alert than they are normally. Make sure you know how you react to phenytoin before you drive, use machines, or do anything else that could be dangerous if you are dizzy or are not alert and able to see well.
Do not stop using phenytoin without first checking with your doctor. Stopping the medicine suddenly may cause your seizures to return or to occur more often.
If you or your child develop a skin rash, hives, or any allergic reaction to phenytoin, tell your doctor or nurse as soon as possible.
Tell your doctor right away if you or your child develop a fever, rash, swollen, painful, or tender lymph glands in the neck, armpit, or groin, unusual bleeding or bruising, or yellow eyes or skin after receiving phenytoin. These may be symptoms of a serious and life-threatening condition called Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS).
Phenytoin may cause liver damage. Check with your doctor right away if you have pain or tenderness in the upper stomach, pale stools, dark urine, loss of appetite, nausea, vomiting, or yellow eyes or skin.
Phenytoin may cause purple glove syndrome. Tell your doctor right away if you or your child have skin discoloration, pain, or swelling at the injection site after receiving phenytoin.
Phenytoin may affect blood sugar levels. If you or your child notice a change in the results of your blood or urine sugar tests or if you have any questions, check with your doctor.
If you or your child develop any unusual or strange thoughts and behavior while receiving phenytoin injection, be sure to discuss it with your doctor. Some changes that have occurred in people receiving phenytoin are like those seen in people who drink too much alcohol. Other changes might be confusion, worsening of depression, hallucinations (seeing, hearing, or feeling things that are not there), suicidal thoughts, and unusual excitement, nervousness, or irritability.
Birth control pills may not work while you are using phenytoin. To keep from getting pregnant, use another form of birth control along with your birth control pills. Other forms include a condom, a diaphragm, or a contraceptive foam or jelly.
Avoid drinking alcohol while you are receiving phenytoin.
Before you have any medical tests, tell the medical doctor in charge that you or your child are taking phenytoin. The results of some tests may be affected by phenytoin.
Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.
Phenytoin side effects
Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.
Check with your doctor or nurse immediately if any of the following side effects occur:
- Chest pain or discomfort
- cold, clammy, or pale skin
- decreased coordination
- difficulty with sleeping
- drowsiness to profound coma
- fast, slow, or irregular heartbeat
- measles-like skin rash
- mood or other mental changes
- pain in the shoulders, back, neck, or jaw
- shakiness and unsteady walk
- slow heart rate
- slurred speech
- swelling of the feet and lower legs
- troubled breathing
- uncontrolled eye movements
- unsteadiness, trembling, or other problems with muscle control or coordination
- unusual tiredness or weakness
- Bleeding, blistering, burning, coldness, discoloration of the skin, feeling of pressure, hives, infection, inflammation, itching, lumps, numbness, pain, rash, redness, scarring, soreness, stinging, swelling, tenderness, tingling, ulceration, or warmth at the injection site
- blistering, crusting, irritation, itching, peeling, or reddening of the skin
- cracked, dry, or scaly skin
- inability to move the eyes
- increased blinking or spasms of the eyelid
- shakiness in the legs, arms, hands, or feet
- sticking out of the tongue
- trouble with breathing, speaking, or swallowing
- twitching, uncontrolled movements of the tongue, lips, face, neck, trunk, arms, or legs
- unusual facial expressions
Incidence not known
- Abdominal or stomach pain
- bleeding gums
- blisters, hives, or itching
- bloating of the abdomen or stomach
- blood in the urine or stools
- bloody, black, or tarry stools
- blurred vision
- break in the skin, especially associated with blue-black discoloration, swelling, or drainage of fluid
- burning, numbness, tingling, or painful sensations
- cough or hoarseness
- dark urine
- dizziness, faintness, or lightheadedness when getting up suddenly from a lying or sitting position
- fainting spells
- fever with or without chills
- general feeling of discomfort or illness
- general feeling of tiredness or weakness
- hair loss
- high fever
- irritation in the mouth
- joint or muscle pain
- light-colored stools
- loss of appetite
- loss of heat from the body
- lower back or side pain
- muscle or joint pain
- painful or difficult urination
- pale skin
- pinpoint red spots on the skin
- red skin lesions, often with a purple center
- red, irritated eyes
- red, swollen skin
- redness and swelling of the gums
- skin rash
- sore throat
- soreness of the muscles
- sores, ulcers, or white spots on the lips or in the mouth
- stomach pain, continuing
- swollen glands
- swollen, painful, or tender lymph glands in the neck, armpit, or groin
- unexplained bleeding or bruising
- unsteadiness or awkwardness
- unusual bleeding or bruising
- weakness in the arms, hands, legs, or feet
- weight loss
- yellow eyes or skin
Get emergency help immediately if any of the following symptoms of overdose occur:
Symptoms of overdose
- Change in consciousness
- changes in patterns and rhythms of speech
- loss of consciousness
- pounding in the ears
- unusual drowsiness, dullness, tiredness, weakness, or feeling of sluggishness
Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:
Incidence not known
- Difficulty having a bowel movement (stool)
- enlarged lips
- feeling of constant movement of self or surroundings
- increased hair growth on the forehead, back, arms, and legs
- pain of the penis on erection
- sensation of spinning
Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.
Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.
More about phenytoin
- Side Effects
- During Pregnancy or Breastfeeding
- Dosage Information
- Drug Images
- Drug Interactions
- Compare Alternatives
- Pricing & Coupons
- 100 Reviews
- Drug class: group I antiarrhythmics
- Patient Information
- Phenytoin injection
- Phenytoin (Advanced Reading)
- Phenytoin Chewable Tablets
- Phenytoin Extended-Release Capsules
- Phenytoin Suspension
Related treatment guides
Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.