Dilantin Infatabs, Dilantin-125

Introduction

Written by Julz Richterman, PharmD, MBA, BCGP
Medically reviewed by Patricia Weiser, PharmD
Updated on September 23, 2023

Phenytoin (FEN i toyn) is a generic medication prescribed to treat and help prevent certain seizures in adults and children. Phenytoin belongs to a group of drugs called antiepileptic drugs.

The Food and Drug Administration (FDA) has approved phenytoin to treat and help prevent:

• certain types of tonic-clonic seizures
• complex partial seizures
• seizures that occur during or following neurosurgery

These approved uses differ based on the form of phenytoin your doctor prescribes.

This article doesn’t provide coupons for all forms of phenytoin. To find coupons for phenytoin chewable tablet, see this article.

Boxed warning: Risk of cardiovascular problems with rapid infusion of phenytoin injection

Phenytoin injection has a boxed warning about the risk of cardiovascular (heart and blood vessel) problems with rapid infusion of phenytoin injection. An infusion is an injection given over time. Boxed warnings are the most serious warnings from the FDA.

For details, see the “Interactions and warnings for phenytoin” section.

Side effects of phenytoin

Phenytoin may cause mild or serious side effects. More common mild side effects of phenytoin and its serious side effects are listed below. This article doesn’t include all possible side effects of the drug. Side effects can vary based on your age, overall health, and any other medications you take.

To learn more about phenytoin’s side effects, ask your doctor or pharmacist. You can also refer to the prescribing information for phenytoin listed in the “Resources” section.

Mild side effects

More common mild side effects reported with some forms of phenytoin are listed below.

This article doesn’t include all possible mild side effects of the drug. To learn more about phenytoin’s side effects based on the form, refer to the prescribing information for phenytoin listed in the “Resources” section.

With many drugs, mild side effects may go away within a few days or a couple of weeks. If the side effects are bothersome, tell your doctor or pharmacist. They may be able to suggest ways to manage them.

Phenytoin’s mild side effects include:

• sleepiness
• confusion
• decreased coordination
• involuntary eye movement (eyes moving rapidly side-to-side, up-and-down, or in a circle)
• mild allergic reaction*

* For details about this side effect, see the “Interactions and warnings for phenytoin” section.

Serious side effects

Serious side effects of phenytoin are listed below. These side effects may differ based on the form of phenytoin you’re prescribed.

This article doesn’t include all possible serious side effects of the drug. To learn more about phenytoin’s side effects based on the form, refer to the prescribing information for phenytoin listed in the “Resources” section.

With many drugs, serious side effects are possible but not common. If you have serious side effects from this drug, call your doctor right away. If you’re having severe symptoms or a medical emergency, call 911 or a local emergency number.

In general, phenytoin’s serious side effects include:

• severe and potentially life threatening skin reactions
• problems making parts of your blood, including platelets, red blood cells, and white blood cells
• suicidal thoughts or behaviors
• boxed warning: risk of cardiovascular problems with rapid infusion of phenytoin injection*
• severe allergic reaction*

* For details about this side effect, see the “Interactions and warnings for phenytoin” section.

Suicide prevention

If you or someone you know is in crisis and considering suicide or self-harm, please seek support:

• Call the 988 Suicide and Crisis Lifeline at 988.
• Text HOME to the Crisis Textline at 741741.
• Not in the United States? Find a helpline in your country with Befrienders Worldwide.
• Call 911 or your local emergency services number if you feel safe to do so.

If you’re calling on behalf of someone else, stay with them until help arrives. You may remove weapons or substances that can cause harm if you can do so safely.

If you are not in the same household, stay on the phone with them until help arrives.

Common questions about phenytoin

Below you’ll find answers to a few commonly asked questions about phenytoin.

What brand names are available for phenytoin?

Phenytoin is a generic medication. Available brand name versions include:

• Dilantin, which comes as an extended-release (ER)* oral capsule and an oral suspension (a type of liquid mixture)
• Dilantin Infatab, which comes as a chewable tablet
• Phenytek, which comes as an ER oral capsule

Phenytoin injection is not available in a brand-name version.

A generic medication is an identical copy of the active drug in a brand-name medication. (An active drug is the ingredient that makes a medication work.) Generic drugs are believed to be as effective and safe as brand-name drugs. And generic drugs typically cost less compared to brand-name drugs.

Talk with your doctor or pharmacist to learn more about the differences between generic and brand-name medications.

* “Extended-release” means the drug is slowly released into your body over a long period of time.

How does phenytoin work? And how long does it take to start working?

Experts don’t fully understand phenytoin’s mechanism of action (how it works) for treating and helping prevent seizures. The drug attaches to channels (certain proteins) that let sodium in and out of neurons (nerve cells) in your brain. This is thought to stop bursts of nerve signaling that occur during a seizure.

Phenytoin starts working within minutes to hours depending on the form you’re prescribed. But it can take 7–10 days to reach full effect.

If you’d like to know more about this, talk with your doctor or pharmacist.

How does phenytoin compare to Keppra?

Phenytoin and levetiracetam (Keppra) are both antiepileptic drugs. They’re used to treat and help prevent certain types of seizures in adults and children. But they differ in several ways.

For example, one key difference between phenytoin and Keppra is that phenytoin interacts with many different medications. Keppra, on the other hand, has few known interactions. This is just one factor that doctors may consider when choosing to prescribe phenytoin versus Keppra.

In some situations, these drugs may be prescribed together to treat or help prevent certain types of seizures.

Talk with your doctor to learn more about how these drugs compare. They can also determine if one of these medications may be right for you.

Uses of phenytoin

The Food and Drug Administration (FDA) approves prescription drugs such as phenytoin for certain conditions. Approved uses for phenytoin are described below. These uses differ based on the form of phenytoin prescribed.

Use for seizures

Doctors may prescribe phenytoin oral suspension (a liquid mixture), oral capsule, chewable tablet, and injection* for treating and helping prevent certain seizures. These include:

• tonic-clonic seizures (seizure with muscle spasms and loss of consciousness)
• complex partial seizures  (seizure that starts in one part of the brain)
• seizures that occur during or following neurosurgery

Phenytoin injection is also used to treat and help prevent a certain type of tonic-clonic seizure called status epilepticus. Status epilepticus is a severe seizure that doesn’t stop. It’s also used short term when oral forms of phenytoin cannot be used.

Phenytoin is used for these purposes in children under 18 years and adults. It may be prescribed as a short-term or long-term treatment.

A seizure is a burst of electrical signaling in your brain. This unusual increase in activity may cause the following symptoms:

• confusion
• spacing or zoning out
• uncontrollable jerking of your arms, legs, or other parts of your body
• loss of consciousness or awareness
• changes in mood or emotions

The type of seizure you have depends on how much and which part of your brain is involved.

Phenytoin is prescribed by itself or together with other antiepileptic drugs.

* Phenytoin injection is typically given as an intravenous (IV) infusion (an injection given into your vein over time).

Interactions and warnings for phenytoin

Below you’ll find information about phenytoin’s possible interactions and warnings.

Interactions of phenytoin

Certain things may affect how a drug works. These include getting vaccines, consuming alcohol or certain foods, or taking the drug with other medications. This effect is called a drug interaction.

Before you take phenytoin, ask your doctor to check for possible interactions. Be sure to tell them about any of the following you take or use:

• prescription or over-the-counter drugs
• vitamins, herbs, or supplements

To learn about drug-condition interactions, see the “Warnings for phenytoin” section below.

Warnings for phenytoin

Some people should not take phenytoin, and others should take it cautiously.

Boxed warning: Risk of cardiovascular problems with rapid infusion of phenytoin injection

Phenytoin has a boxed warning about the risk of cardiovascular (heart and blood vessel) problems with rapid infusion of phenytoin injection. Boxed warnings are the most serious warnings from the Food and Drug Administration (FDA).

Phenytoin may be given by intravenous (IV) infusion (an injection into your vein given over time). If it is given too quickly, it can cause severe low blood pressure, slow heart rate, or an irregular heartbeat. These can be severe enough to cause heart attack or death. But this is more likely to occur in older adults (ages 65 or older) or in people with certain severe conditions.

More mild symptoms may include dizziness, fainting, lightheadedness, or shortness of breath.

Phenytoin infusions are generally given in a healthcare setting, like a hospital. If you experience any of the above symptoms, tell your doctor or another healthcare professional. They’ll likely want to monitor you further.

To learn more, talk with your doctor or pharmacist.

Other warnings

Phenytoin could cause harm to people with certain health conditions. This effect is called a drug-condition interaction. Other factors can also affect whether phenytoin is a safe option for you. These warnings may differ based on the form of phenytoin you’re prescribed.

Ask your doctor about specific warnings for phenytoin, and be sure to tell your doctor about your:

• current health, including any allergies to medications
• past health conditions or surgeries

Allergic reaction

Phenytoin can cause an allergic reaction in some people. Severe allergic reactions are rare but possible.

If you’ve had an allergic reaction to phenytoin or any of its ingredients, your doctor will likely not prescribe phenytoin. They can tell you about medications that are safer options for you.

A mild allergic reaction may cause the following symptoms:

• skin rash
• itchiness
• flushing (temporary warmth, redness, or deepening of skin color)

A severe allergic reaction may cause the following symptoms:

• swelling under your skin, usually in your hands, feet, eyelids, or lips
• swelling of your mouth, throat, or tongue, which can cause breathing problems

If you have an allergic reaction to phenytoin, call your doctor right away. If you have severe symptoms, call 911 or a local emergency number.

Overdose of phenytoin

If you take phenytoin by mouth, you should not take more phenytoin than your doctor prescribes. For some drugs, doing so may lead to harmful effects or overdose.

If you think you’ve taken too much phenytoin, call your doctor or pharmacist right away. Or you could call 800-222-1222 to speak with someone at America’s Poison Centers. You can also use its online resource. If you have concerning symptoms, call 911 or a local emergency number immediately. You can also go to the closest emergency room.

Pregnancy or breastfeeding and phenytoin

Information about phenytoin and pregnancy and breastfeeding is described below.

Phenytoin and pregnancy

There are risks to taking phenytoin during pregnancy. But there are also risks with having unmanaged seizures while pregnant. (Keep in mind that phenytoin is used for treating and helping prevent seizures.)

If you’re planning a pregnancy or can become pregnant, talk with your doctor about your seizure treatment options during pregnancy. Together, you can discuss the risks and benefits of your treatment options and decide whether or not you should take phenytoin during pregnancy.

Phenytoin and breastfeeding

Phenytoin passes into breast milk. There are risks to taking phenytoin while breastfeeding. But there are also risks with having unmanaged seizures during this time. (Keep in mind that phenytoin is used for treating and helping prevent seizures.)

If you’re planning to breastfeed, talk with your doctor about your seizure treatment options. Together, you can discuss the risks and benefits of your treatment options and decide whether or not you should take phenytoin during this time. Your doctor may recommend other healthy ways to feed your child.

What to ask your doctor

Let your doctor know if you have questions about phenytoin or would like more details about it.

Here’s a list of some possible questions you may want to ask your doctor:

• Does phenytoin interact with any of my other medications?
• Can I drink alcohol while taking phenytoin?
• What should I do if I miss a dose?
• Will I ever be able to stop taking phenytoin?
• Is it safe for me to take dietary supplements with phenytoin?

Resources

• Food and Drug Administration. (2023). Orange Book: Approved drug products with therapeutic equivalence evaluations. https://www.accessdata.fda.gov/scripts/cder/ob/index.cfm
• Keppra (levetiracetam) tablets, for oral use Keppra (levetiracetam) oral solution. (2023). https://www.accessdata.fda.gov/drugsatfda_docs/label/2023/021035s113,021505s052lbl.pdf
• Phenytoin sodium — phenytoin sodium capsule, extended release. (2023). https://nctr-crs.fda.gov/fdalabel/services/spl/set-ids/7f20cf98-1a63-4eaf-a7ac-fa5d79a045e0/spl-doc
• Phenytoin sodium — phenytoin sodium injection. (2022). https://nctr-crs.fda.gov/fdalabel/services/spl/set-ids/a4f31068-73fb-4efb-b4ac-7d1b9fd9f79a/spl-doc
• Phenytoin — phenytoin suspension. (2023). https://nctr-crs.fda.gov/fdalabel/services/spl/set-ids/3cac9830-f71e-4111-b116-47f23077c21d/spl-doc
• Phenytoin — phenytoin tablet, chewable. (2023). https://nctr-crs.fda.gov/fdalabel/services/spl/set-ids/31e8a777-75b1-4f48-9682-0bcc3189ad26/spl-doc

Disclaimer: Optum Perks has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.