May 24, 2024

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Dilantin (Phenytoin) Oral: Uses, Side Effects, Dosages

16 min read

What Is Dilantin?

Dilantin (phenytoin) belongs to a class of drugs called anticonvulsants, also known as anti-seizure or anti-epileptic drugs. This oral prescription medication is used to prevent and treat certain types of seizures (convulsions) and is available as an extended-release capsule, chewable tablet, or liquid syrup.

Dilantin works by slowing down nerve impulses in the brain to control and prevent seizure activity.

Drug Facts

  • Generic Name: Phenytoin
  • Brand Name(s): Dilantin, Dilantin-125, Dilantin Infatabs, Phenytek
  • Administration Route(s): Oral
  • Drug Availability: Prescription
  • Therapeutic Classification: Anticonvulsant
  • Available Generically: Yes
  • Controlled Substance: N/A
  • Active Ingredient: Phenytoin
  • Dosage Form(s): Tablet, suspension, capsule

What Is Dilantin Used For?

Dilantin is used to prevent and control certain types of seizures, specifically focal (affecting one side of the brain) and generalized (affecting both sides of the brain) seizures.

It’s also used to prevent and treat seizures that occur during or after brain surgery.

How to Take Dilantin

Dilantin is available as a chewable tablet, extended-release (long-acting) capsule, and liquid formulation.

If it upsets your stomach, you can take Dilantin with meals. However, you should avoid taking antacids at the same time as Dilantin. Antacids can make it difficult for your body to absorb the drug. Your prescriber will likely need to take labs and draw blood from you periodically to determine the right maintenance dose for you.

If you receive Dilantin through a feeding tube, stop the tube feeds for two hours before taking the Dilantin. Then, wait two hours after taking the Dilantin before restarting the tube feeds.

Extended-Release Capsules

If you are taking the extended-release capsules, swallow them whole with a full glass of water. Do not chew, break, or crush them.

Chewable Tablets

Chewable tablets are a good option for children or adults who have trouble swallowing capsules, although, if preferred, they can be swallowed whole with a full glass of water.

Liquid Form

If you are taking the liquid form of Dilantin, shake the bottle well before each use and use the dosing syringe, spoon, or cup provided by the pharmacist. Do not use a kitchen spoon or another device from home, as this can lead to accidental over or underdosing.

It’s always important to take Dilantin exactly as directed by your healthcare provider. Never stop taking the drug on your own or take it more or less often than directed. 

Do not stop taking Dilantin suddenly, as this increases your risk for developing seizures that don’t stop (called status epilepticus).


Keep the Dilantin liquid suspension and extended-release capsules in a tightly closed, light-resistant container. Do not freeze the liquid suspension.

Keep all formulations away from moisture, and store them at room temperature or between 68 F and 77 F. Make sure that your medication is out of reach of children and pets.

Off-Label Uses

Healthcare providers can prescribe Dilantin off-label to treat conditions that are not listed on the product label. This doesn’t mean that Dilantin is not effective for these conditions. Healthcare providers decide to prescribe drugs off-label based on scientific evidence and expert medical judgment.

Dilantin can be used off-label to treat:

How Long Does Dilantin Take to Work?

How high your dose is will affect the way your body processes phenytoin. While you may begin to see a benefit sooner, it takes seven to 10 days for levels of the drug to normalize in the body.

What Are the Side Effects of Dilantin?

This is not a complete list of side effects and others may occur. A medical professional can advise you on side effects. If you experience other effects, contact your pharmacist or a medical professional. You may report side effects to the FDA at or 1-800-FDA-1088.

Like other medications, Dilantin can cause side effects. Talk to your healthcare provider about any side effects you experience while taking this medication.

Common Side Effects

Common side effects include:

  • Balance and walking problems
  • Slurred speech
  • Irregular movements of the eyes 
  • Confusion
  • Dizziness
  • Trouble sleeping
  • Nervousness
  • Tremors
  • Headache
  • Upset stomach and throwing up
  • Constipation
  • Rash

Severe Side Effects

Serious side effects may occur when taking Dilantin.

Knowing which ones warrant an immediate call to a medical professional vs. calling 911 or going to the nearest emergency room is helpful. That said, only basic guidance, not medical advice, is provided below. Always call 911 if you think your symptoms are potentially life-threatening.

Like all anticonvulsant drugs, Dilantin may increase your risk for suicidal thoughts and behavior.

Call your healthcare provider if you experience:

  • Depression, anxiety, or irritability that is new or getting worse
  • Agitation or restlessness
  • Trouble sleeping
  • Panic attacks
  • Angry, violent, aggressive, or impulsive outbursts
  • Symptoms of mania (e.g., extreme energy or talking excessively fast)
  • Any unusual or sudden changes in behavior or mood

Dilantin may also cause serious lymph node, blood, liver, or heart problems.

Call your provider if you have:

  • Swollen lymph nodes
  • Frequent infections, or infections that won’t go away
  • Severe or unusual tiredness or weakness
  • Easy or unusual bruising or bleeding
  • New rash and/or purple or red spots on your skin
  • Yellowing of your skin or eyes (jaundice) 
  • Pain on the right side of your abdomen
  • Dizziness or feeling like you might faint
  • Chest pain or pressure
  • Slow or irregular heartbeat

A metallic taste in your mouth or high blood sugar may also occur as a result of taking Dilantin. Let your provider know if you have increased thirst/urination, flushing, unusual sleepiness, and/or breath that smells fruity or sweet.

Call 911 or go to your nearest emergency room if you or someone you know is experiencing:

  • Thoughts of or attempts at suicide
  • Signs of a potentially fatal skin reaction to Dilantin (e.g., red rash, blisters and sores on the skin and in the mouth or eyes, and/or peeling skin)
  • Signs of a severe allergic reaction to Dilantin (e.g., swelling of the face, eyes, lips, or tongue, or difficulty in swallowing or breathing)

Of note, people with certain genes—for example, HLA-B*1502—have a greater chance of experiencing a severe skin reaction to Dilantin. To prevent these reactions from occurring, a provider may test you for this gene before you begin taking Dilantin.

Long-Term Side Effects

If you take Dilantin for months or years, especially at high doses, you are at risk for developing certain effects:

  • Overgrowth of your gums (gingival hyperplasia)
  • Excessive hair on your body or face
  • Acne
  • Coarseness of facial features

Children and young adults taking Dilantin are more likely to develop gingival hyperplasia. Brushing and flossing your teeth and seeing a dentist on a regular basis can help prevent this complication.

In addition, taking Dilantin for a long time puts you at risk of developing bone softening (osteomalacia) and bone weakening (osteoporosis). These conditions may cause bone pain, muscle weakening, and bone breaks (fractures).

To monitor for these complications, a healthcare provider may periodically check your vitamin D level or order a bone mineral density test.

Lastly, some people who take Dilantin for several years may develop nerve damage in their legs or damage to a region of the brain called the cerebellum.

Dosage: How Much Dilantin Should I Take?

Drug Content Provided and Reviewed by IBM Micromedex

The dose of this medicine will be different for different patients. Follow your doctor’s orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

For seizures:

For oral dosage form (extended-release capsules):

  • Adults—At first, 100 milligrams (mg) 3 times a day or 300 mg once a day. Your doctor may increase your dose as needed. For patients in the clinic or hospital (except with a history of liver or kidney disease), a loading dose of 1000 mg is divided into three doses (400 mg, 300 mg, 300 mg) and given every 2 hours. Then, normal maintenance dose may be started 24 hours after the loading dose.
  • Children older than 6 years of age—300 mg per day. Your doctor may adjust your dose as needed.
  • Children 6 years of age and younger—Dose is based on body weight and must be determined by your doctor. At first, 5 milligrams (mg) per kilogram (kg) of body weight given in 2 or 3 divided doses per day. The doctor may adjust the dose as needed.

For oral dosage form (suspension):

  • Adults—At first, 5 milliliters (mL) or one teaspoonful 3 times a day. Your doctor may adjust your dose as needed. However, the dose is usually not more than 25 mL per day.
  • Children older than 6 years of age—300 mg per day. Your doctor may adjust your dose as needed.
  • Children 6 years of age and younger—Dose is based on age and body weight and must be determined by your doctor. At first, 5 milligrams (mg) per kilogram (kg) of body weight given in 2 or 3 divided doses per day. Your doctor may adjust your dose as needed.

For oral dosage form (tablets):

  • Adults—At first, 100 milligrams (mg) 3 times a day. Your doctor may adjust your dose as needed.
  • Children older than 6 years of age—300 mg per day, given in 2 or 3 divided doses per day. Your doctor may adjust your dose as needed.
  • Children 6 years of age and younger—Dose is based on age and body weight and must be determined by your doctor. At first, 5 milligrams (mg) per kilogram (kg) of body weight given in 2 or 3 divided doses per day. The doctor may adjust the dose as needed.


In some cases, your healthcare provider may change the dose of your medication.


For children aged 6 and younger, Dilantin is always dosed by age and body weight. 

For older patients (aged 65 years and older), there are no specific dosing adjustments. However, since Dilantin may take longer to be processed in the bodies of older patients, lower and/or less frequent doses are generally used.


If you are pregnant or planning on becoming pregnant, talk to your healthcare provider. Dilantin, like other anti-seizure medications, has been linked to both physical and mental birth defects.

The good news is that emerging research has found that newer anti-seizure drugs, notably Lamictal and Keppra, are associated with a much lower rate of birth defects. To ensure optimal seizure control and the safety of your baby, it’s best to talk with your medical provider well before pregnancy about the best anti-seizure drug to use.

Also, if you take Dilantin or another anti-seizure drug while pregnant, know that you will need extra monitoring. With Dilantin, your dose will probably need to be increased to keep the blood level the same as it was before pregnancy. You may be asked to enroll in a registry that collects information about the safety of medications like Dilantin during pregnancy. This recommendation is standard practice.


When you are pregnant, it’s also important to talk with your provider if you are thinking about breastfeeding, as Dilantin does pass into breast milk. Together, you and your provider can make the best decision for you and your baby’s health.

Missed Dose

If you miss a dose of your Dilantin, take it as soon as possible, unless it’s almost time for your next dose. In that case, skip the missed dose and take your Dilantin at the next regularly scheduled time.

As a reminder, don’t double your doses. If you find that you are missing doses often, consider using a pill container or calendar, or setting an alarm on your phone or watch.

Overdose: What Happens If I Take Too Much Dilantin?

Symptoms of a Dilantin overdose may include unusual eye movements, balance or coordination problems, and difficulty speaking.

What Happens If I Overdose on Dilantin?

If you think you or someone else may have overdosed on Dilantin, call a healthcare provider or the Poison Control Center (1-800-222-1222).

If someone collapses or isn’t breathing after taking Dilantin, call 911 immediately.


Drug Content Provided and Reviewed by IBM Micromedex

It is very important that your doctor check your or your child’s progress at regular visits while using this medicine to see if it is working properly and to allow for a change in the dose. Blood and urine tests may be needed to check for any unwanted effects.

Using this medicine 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 use this medicine if you or your child are also using delavirdine (Rescriptor®). Using these medicines together may cause unwanted effects.

Lymph node problems may occur while using this medicine. Check with your doctor right away if you or your child have swollen, painful, or tender lymph glands in your neck, armpit, or groin.

Do not stop using this medicine without first checking with your doctor. Your doctor may want you or your child to gradually reduce the amount you are using before stopping completely.

This medicine may cause serious allergic reactions, including angioedema. These can be life-threatening and require immediate medical attention. Tell your doctor right away if you or your child have a rash, itching, hoarseness, trouble breathing, trouble swallowing, or any swelling of your hands, face, or mouth after using this medicine.

Serious skin reactions can occur with this medicine. Check with your doctor right away if you or your child have blistering, peeling, or loose skin, red skin lesions, severe acne or skin rash, sores or ulcers on the skin, a fever, or chills while you are using this medicine.

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 using this medicine. These may be symptoms of a serious and life-threatening condition called drug reaction with eosinophilia and systemic symptoms (DRESS).

Phenytoin may cause heart problems, including a slow heartbeat. Check with your doctor right away if you have chest pain, dizziness, or tiredness.

This medicine 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 can temporarily lower the number of white blood cells in your blood, increasing the chance of getting an infection. It can also lower the number of platelets, which are necessary for proper blood clotting. If this occurs, there are certain precautions you can take, especially when your blood count is low, to reduce the risk of infection or bleeding:

If you can, avoid people with infections. Check with your doctor immediately if you think you are getting an infection or if you get a fever or chills, cough or hoarseness, lower back or side pain, or painful or difficult urination.

Check with your doctor immediately if you notice any unusual bleeding or bruising, black, tarry stools, blood in the urine or stools, or pinpoint red spots on your skin.

Be careful when using a regular toothbrush, dental floss, or toothpick. Your medical doctor, dentist, or nurse may recommend other ways to clean your teeth and gums. Check with your medical doctor before having any dental work done.

Do not touch your eyes or the inside of your nose unless you have just washed your hands and have not touched anything else in the meantime.

Be careful not to cut yourself when you are using sharp objects such as a safety razor or fingernail or toenail cutters.

Avoid contact sports or other situations where bruising or injury could occur.

This medicine may decrease bone mineral density. A low bone mineral density can cause weak bones or osteoporosis. If you or your child have any questions about this, ask your doctor.

This medicine 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.

This medicine may cause some people to be agitated, irritable, or display other abnormal behaviors. It may also cause some people to have suicidal thoughts and tendencies or to become more depressed. If you, your child, or your caregiver notice any of these side effects, tell your or your child’s doctor right away.

In some patients (usually younger patients), tenderness, swelling, or bleeding of the gums (gingival hyperplasia) may appear soon after phenytoin treatment is started. To help prevent this, brush and floss your teeth carefully and regularly and massage your gums. Also, see your dentist every 6 months to have your teeth cleaned. If you have any questions about how to take care of your teeth and gums, or if you notice any tenderness, swelling, or bleeding of your gums, check with your doctor or dentist.

Before you have any medical tests, tell the medical doctor in charge that you or your child are taking this medicine. The results of some tests may be affected by this medicine.

This medicine may cause drowsiness, trouble thinking, or trouble in controlling movements. Do not drive or do anything else that could be dangerous until you know how this medicine affects you.

Avoid drinking alcohol while you are using this medicine.

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.

What Are Reasons I Shouldn’t Take Dilantin?

You should not take Dilantin if you have a known allergy to phenytoin or any of its ingredients, or to one or more of the following anticonvulsant drugs:

  • Cerebyx (fosphenytoin)
  • Peganone (ethotoin)
  • Mesantoin (mephenytoin)

Do not use Dilantin with the HIV antiviral drug Rescriptor (delavirdine). 

Dilantin should be used cautiously in patients with a history of liver disease, diabetes, depression, a slow heartbeat, or a rare condition called porphyria.

What Other Medications Interact With Dilantin?

There are several medications that may interact with Dilantin. If you are taking a medicine that interacts with Dilantin, your provider may need to adjust your dose, choose an alternative medicine, and/or order special tests for monitoring purposes.

This is not a complete list, but some drugs that may increase the blood levels of Dilantin in your body include:

This is also not a complete list, but some medications that can decrease the blood levels of Dilantin in your body include:

Dilantin may also alter the blood concentrations of other medications.

Examples of these medications include: 

Lastly, blood levels of Dilantin may be lower than expected in patients who are receiving tube feedings.

Before starting Dilantin, tell your healthcare provider all of the drugs you are taking, including prescription and over-the-counter medications, herbal products, supplements, vitamins, and recreational drugs.

What Medications Are Similar?

Besides Dilantin, there are other anticonvulsants that your healthcare provider may consider prescribing.

Dilantin controls and prevents seizures by blocking sodium channels which reduces waves of abnormal electrical activity from spreading throughout the brain. Other anti-seizure drugs that work by interacting with sodium channels include Lamictal (lamotrigine) and Tegretol (carbamazepine).

Deciding which anti-seizure medication (or combination, in some cases) is best for you depends on factors such as the drug’s side effects and dosing/monitoring schedule, and how it interacts with other drugs.

Frequently Asked Questions

  • What is Dilantin used for?

    Dilantin treats focal (affecting one side of the brain) and generalized (affecting both sides of the brain) seizures. It’s also approved to prevent and treat seizures that occur during or after brain surgery.

    Sometimes, Dilantin is prescribed off-label to treat a nerve pain disorder called trigeminal neuralgia or to prevent seizures that may occur soon after a head injury.

  • What are the short-term effects of taking Dilantin?

    There are many potential side effects of Dilantin, some more serious than others, like skin, liver, or blood problems. Some of the more common side effects associated with Dilantin are related to your nervous system.

    Rarely, Dilantin may cause suicidal thoughts or actions. Seek medical attention if you are developing any new, worsening, or worrying mental or mood symptoms while taking Dilantin.

  • What are the long-term effects of taking Dilantin?

    Long-term use of Dilantin may also cause an overgrowth of your gum tissue—what’s known as gingival hyperplasia. This is more common in children. Brushing and flossing daily and seeing your dentist on a regular basis can help prevent this.

    Osteoporosis may also occur with chronic use of Dilantin. If you are on Dilantin for a long time, your healthcare provider will probably ask you to take calcium and vitamin D supplements to help strengthen your bones.

  • Can I take Dilantin during pregnancy?

    Taking anti-seizure medications, including Dilantin, during pregnancy has been linked to both physical and mental birth defects. Nevertheless, seizure control during pregnancy is essential to keeping the mother and baby safe. There may be other anti-seizure treatment options with a lower rate of birth defects.

  • Can I drink alcohol while taking Dilantin?

     Alcohol may change the level of Dilantin in your bloodstream, especially if large amounts of alcohol are consumed. This can put you at risk of having a seizure. As a result, your healthcare provider will probably advise you to not drink alcohol while you are on Dilantin.

How Can I Stay Healthy While Taking Dilantin?

While not always easy, staying healthy when taking Dilantin means adopting a “take charge” attitude about your health care and overall well-being.

This starts with taking your Dilantin exactly as instructed by your healthcare provider. Your brain needs a consistent supply of medication to prevent seizures.

Other practices you should strongly consider include:

It’s also important to not miss any of your appointments with your healthcare team and keep up with your bloodwork. Regular bloodwork is necessary to ensure a stable level of Dilantin in your bloodstream.

Always remember to be open and honest with your healthcare providers about how you are feeling and what you are thinking. Whether you are bothered by a particular side effect, feeling emotionally drained, or contemplating a major life change, like pregnancy, nothing is too insignificant to share and discuss.

Medical Disclaimer

Verywell Health’s drug information is meant for education purposes only and not intended as a replacement for medical advice, diagnosis, or treatment from a healthcare professional. Consult your doctor before taking any new medication(s). IBM Watson Micromedex provides some of the drug content, as indicated on the page.

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