This article describes possible side effects of phenytoin injection. You can explore this overview article to learn more about phenytoin, including the drug’s uses, ways to save on cost, and more.
Phenytoin injection is a generic medication. It isn’t available in a brand-name version. Phenytoin also comes in forms that you swallow, but these forms aren’t described in this article. To learn more about these forms, talk with your doctor.
Boxed warning: Risk of cardiovascular problems with rapid infusion
Phenytoin injection has a boxed warning for the risk of cardiovascular (related to the heart and blood vessels) problems with rapid infusion. A boxed warning is the most serious warning from the Food and Drug Administration (FDA).
For details, see the “Side effects of phenytoin in detail” section below.
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More common side effects of phenytoin
Phenytoin injection may cause mild or serious side effects. Below are some of the more common side effects of this medication.
Commonly reported side effects of phenytoin injection include:
- nystagmus (involuntary eye movements)
- problems with balance or coordination
- slurred speech
- sleepiness
- confusion
Mild side effects of phenytoin
Phenytoin may cause certain mild side effects. Usually, mild side effects are temporary and can be easily managed. Tell your doctor or pharmacist if you have side effects that don’t go away or become bothersome.
Mild side effects of phenytoin injection that occurred in studies include:
- decreased coordination
- confusion
- sleepiness
- nystagmus
- rash
- nausea
- vomiting
- constipation
- slurred speech
- dizziness or vertigo
- insomnia (trouble sleeping)
- nervousness
- twitching
- paresthesia (numbness, itchiness, or pins and needles feeling in your arms or legs)
- headache
- metallic taste
- mild allergic reaction*
Phenytoin injection may cause more mild side effects than those listed above. For details, see the drug’s prescribing information.
* To learn more about this side effect, see the “Side effects of phenytoin in detail” section below.
Serious side effects of phenytoin
Phenytoin may cause certain serious side effects. If you have any serious side effects from phenytoin injection, call your doctor right away. But if you think you’re having a medical emergency or your side effects feel life threatening, take immediate action. Call 911 or a local emergency number, or go to the nearest emergency room.
After the FDA approves a drug, it tracks and reviews side effects of the medication. Visit MedWatch’s website if you’d like to notify the FDA about a side effect you’ve had with phenytoin.
Serious side effects of phenytoin injection that occurred in studies include:
- gingival hyperplasia (overgrowth of gum tissue around the teeth)*
- seizures, if phenytoin injection is stopped too suddenly
- serious skin reactions, including Stevens-Johnson syndrome and toxic epidermal necrolysis
- drug reaction with eosinophilia and systemic symptoms (DRESS)
- liver problems*
- atypical blood cell levels
- serious irritation and inflammation where phenytoin is injected
- high blood sugar
- serious heart problems
- involuntary or uncontrollable muscle movements
- cerebellar atrophy (a type of brain dysfunction)
- Peyronie’s disease
- risk of cardiovascular problems with rapid infusion*†
- severe allergic reaction*
* To learn more about this side effect, see the “Side effects of phenytoin in detail” section below.
† Phenytoin injection has a boxed warning for this side effect. A boxed warning is the most serious warning from the FDA. To learn more, see the “Side effects of phenytoin in detail” section below.
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Get free cardSide effects of phenytoin in children
For children, doctors prescribe phenytoin injection to treat and prevent certain types of seizures.
In studies, the following side effects were more common in children than in adults:
- serious cardiovascular problems with rapid infusion*
If you’d like to know more about side effects in children taking phenytoin injection, talk with your doctor or pharmacist.
* Phenytoin injection has a boxed warning for this side effect. A boxed warning is the most serious warning from the FDA. To learn more, see the “Side effects of phenytoin in detail” section below.
Common questions about side effects of phenytoin
Here are answers to some common questions about side effects of phenytoin injection. If you have other questions, talk with your doctor or pharmacist.
Does phenytoin cause long-term side effects?
Yes, in some cases phenytoin injection may cause long-term side effects. These can last for a while after you’ve stopped taking the drug.
Examples of long-term side effects reported with phenytoin injection include:
- liver problems*
- atypical blood cell levels
Talk with your doctor to learn more about these side effects and how to manage them. Ask your doctor for more information about how long these side effects of phenytoin may last.
* To learn more about this side effect, see the “Side effects of phenytoin in detail” section below.
How do side effects of phenytoin seen in females compare with those seen in males?
In studies, side effects of phenytoin were similar in females* and males*. There were no differences in side effects based on sex.
If you have more questions about this, talk with your doctor.
*Sex and gender exist on spectrums. In this article, we use the terms “male” and “female” to refer to a person’s sex assigned at birth.
Can phenytoin be used for bipolar disorder? If so, are the side effects of phenytoin similar when used for seizures compared to bipolar disorder?
Maybe. But phenytoin isn’t approved to treat bipolar disorder. It’s approved to treat certain types of seizures.
In some cases, doctors may prescribe phenytoin off-label for bipolar disorder. With off-label use, doctors prescribe a drug for a purpose other than what it’s approved for.
If you have questions about treatment options for bipolar disorder, talk with your doctor.
Side effects of phenytoin in detail
Below you’ll find details on some of the side effects of phenytoin injection.
Risk of cardiovascular problems with rapid infusion
Phenytoin injection has a boxed warning for the risk of cardiovascular problems with rapid infusion. A boxed warning is the most serious warning from the FDA.
Phenytoin injection can be given by intravenous (IV) infusion, which is an injection given into your vein over time. But if it’s administered too rapidly, it can cause severely low blood pressure and atypical heart rate or rhythms. This risk is especially high for children.
With cardiovascular problems, you can experience symptoms such as:
- fatigue (low energy)
- lightheadedness
- nausea
- loss of consciousness
- blurry vision
- irregular heartbeat
- fluttering feeling in your chest
- chest pain or tightness
- sweating
Certain factors can increase the risk of cardiovascular problems with phenytoin injection. These include:
- critical illness
- being age 65 years or older
- history of low blood pressure
- history of severe heart problems or heart disease
Ways to manage
Due to this risk, your doctor will monitor your heart closely during and after giving you phenytoin injection.
If you experience symptoms of heart problems, tell your doctor. They’ll likely slow down your phenytoin infusion or stop the medication altogether.
Gingival hyperplasia
Gingival hyperplasia (overgrowth of gum tissue around the teeth) occurred in studies of people using phenytoin injection. This side effect can be mild to severe.
With gingival hyperplasia, you have enlargement of your gums. This can cause symptoms such as:
- painful, red, or bleeding gums
- inflammation
- bad breath
Certain factors can increase the risk of gingival hyperplasia with phenytoin injection. These include:
- taking other drugs that cause gingival hyperplasia
- poor oral hygiene
- pregnancy
- hormonal imbalances
Ways to manage
To minimize the risk of gingival hyperplasia, it’s important to practice good oral hygiene. If you have concerns about this side effect, tell your doctor. They can discuss strategies to minimize this risk, as well as alternative treatments.
Liver problems
Phenytoin injection can increase the risk of serious liver problems, including liver failure.
Liver problems can cause symptoms such as:
- tiredness
- loss of appetite
- nausea and vomiting
- yellowing of the skin or eyes
- diarrhea
Certain factors can increase the risk of liver problems with phenytoin injection. These include:
- alcohol use
- taking other drugs that can cause liver problems
- being age 65 years or older
Ways to manage
If you experience symptoms of liver problems, tell your doctor. They’ll likely recommend stopping phenytoin injection.
Allergic reaction
For some people, phenytoin injection can cause an allergic reaction.
Symptoms can be mild or serious, and they may include:
- itchiness
- skin rash
- swelling under the skin, usually affecting eyelids, lips, hands, or feet
- swelling of the mouth, tongue, or throat, which can make it hard to breathe
- flushing (temporary warmth, redness, or deepening of skin color)
Ways to manage
For mild allergic reaction symptoms, such as a mild rash, call your doctor right away. They may recommend treatments to help manage your symptoms. They’ll also let you know whether you should keep taking the medication.
For severe allergic reaction symptoms, such as swelling or trouble breathing, call 911 or your local emergency number right away. These symptoms require immediate medical care because they can become life threatening. If you’ve had a serious allergic reaction to phenytoin injection, your doctor may recommend taking a different medication instead.
Warnings for phenytoin
Below are some factors you may want to discuss with your doctor before taking phenytoin injection.
Boxed warning: Risk of cardiovascular problems with rapid infusion
Phenytoin has a boxed warning for the risk of cardiovascular problems with rapid infusion. A boxed warning is the most serious warning from the FDA.
For details, see the “Side effects of phenytoin in detail” section above.
Other warnings
It may not be safe for you to take phenytoin injection if you have specific health conditions. These are sometimes called drug-condition interactions. Other things may also affect whether phenytoin injection is a safe treatment option for you.
Before taking phenytoin injection, tell your doctor about your health and medications you take. Things to consider include:
- current pregnancy
- history of diabetes
- history of heart, kidney, or liver disease
- alcohol use
- past allergic reaction to phenytoin
Phenytoin and pregnancy
Phenytoin injection should not be used during pregnancy. If you’re planning a pregnancy or can become pregnant, talk with your doctor before using this medication. Your doctor may suggest birth control options to use during treatment with phenytoin.
Phenytoin and breastfeeding
It’s not known whether phenytoin injection should be used while breastfeeding. If you’re currently breastfeeding or planning to do so, talk with your doctor before using this medication.
Phenytoin and alcohol
Phenytoin injection is known to interact with alcohol.
Depending on how much you drink, alcohol can alter the levels of phenytoin in your body. This can increase your risk of side effects or make the medication less effective.
If you drink alcohol, talk with your doctor about whether it’s safe to consume it during your treatment with phenytoin injection.
What to ask your doctor
This article describes common and serious side effects of phenytoin injection. If your doctor prescribes this medication, they can discuss possible side effects with you. Let your doctor know if you have concerns or questions about treatment with this medication.
Here’s a list of some possible questions you may want to ask your doctor:
- Is my risk of gingival hyperplasia greatest when I first start treatment?
- Is it safe to use phenytoin injection if I have diabetes?
- How do the side effects of phenytoin injection compare with the side effects of phenytoin that you take by mouth?
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.