Phenytoin (Oral)

Generic name: Phenytoin

Usage of Phenytoin (Oral)

Phenytoin is used to control seizures (convulsions), including tonic-clonic (grand mal) and psychomotor (temporal lobe) seizures, in the treatment of epilepsy. It is also used to prevent and treat seizures that occur during brain surgery. This medicine is an anticonvulsant that works in the brain tissue to stop seizures.

This medicine is available only with your doctor's prescription.

Phenytoin (Oral) 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 immediately if any of the following side effects occur:

More common

Decreased coordination

mental confusion

nervousness

slurred speech

trouble with breathing, speaking, or swallowing

unsteadiness, trembling, or other problems with muscle control or coordination

Rare

Inability to move the eyes

increased blinking or spasms of the eyelid

shakiness and unsteady walk

shakiness in the legs, arms, hands, or feet

sticking out of the tongue

trembling or shaking of the hands or feet

twitching, twisting, or uncontrolled repetitive movements of the tongue, lips, face, arms, or legs

uncontrolled twisting movements of the neck, trunk, arms, or legs

unusual facial expressions

Incidence not known

Bleeding gums

blistering, peeling, or loosening of the skin

blisters, hives, itching, skin rash

bloating of the abdomen or stomach

blood in the urine or stools

bloody, black, or tarry stools

chest pain or discomfort

chills

cough

dark urine

diarrhea

difficulty with moving

fainting spells

fever with or without chills

general feeling of discomfort or illness

hair loss

headache

high fever

hoarseness

irritation in the mouth

joint or muscle pain

light-colored stools

lightheadedness or dizziness

lower back or side pain

muscle stiffness

nausea

numbness, tingling, or pain in the hands or feet

painful or difficult urination

pale skin

pinpoint red spots on the skin

red skin lesions, often with a purple center

red, irritated eyes

redness and swelling of the gums

slow or irregular heartbeat

sore throat

sores, ulcers, or white spots on the lips or in the mouth

stomach pain

swollen, painful, or tender lymph glands in the neck, armpit, or groin

unusual bleeding or bruising

unusual tiredness or weakness

upper right abdominal or stomach pain

vomiting

weight loss

yellow eyes or skin

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:

More common

Trouble sleeping

uncontrolled eye movements

Incidence not known

Difficulty having a bowel movement

enlarged lips

feeling of constant movement of self or surroundings

increased hair growth on the forehead, back, arms, or 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.

Before taking Phenytoin (Oral)

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 this medicine, the following should be considered:

Allergies

Tell your doctor if you have ever had any unusual or allergic reaction to this medicine 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.

Pediatric

Appropriate studies performed to date have not demonstrated pediatric-specific problems that would limit the usefulness of phenytoin in children.

Geriatric

Appropriate studies performed to date have not demonstrated geriatric-specific problems that would limit the usefulness of phenytoin 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.

Breast Feeding

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 taking this medicine, 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 this medicine 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.

Artemether

Atazanavir

Boceprevir

Cabotegravir

Cobicistat

Daclatasvir

Darunavir

Dasabuvir

Delamanid

Delavirdine

Doravirine

Elbasvir

Elvitegravir

Fostemsavir

Grazoprevir

Isavuconazonium

Lenacapavir

Lorlatinib

Lurasidone

Maraviroc

Mavacamten

Nirmatrelvir

Ombitasvir

Pacritinib

Paritaprevir

Piperaquine

Praziquantel

Ranolazine

Rilpivirine

Ritonavir

Telaprevir

Tenofovir Alafenamide

Using this medicine 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.

Abemaciclib

Abiraterone Acetate

Acalabrutinib

Adagrasib

Afatinib

Alfentanil

Alpelisib

Aluminum Carbonate, Basic

Aluminum Hydroxide

Aluminum Phosphate

Amiodarone

Apazone

Apixaban

Apremilast

Aprepitant

Aripiprazole

Asciminib

Aspirin

Atogepant

Avacopan

Avapritinib

Axitinib

Beclamide

Bedaquiline

Belumosudil

Bendamustine

Benzhydrocodone

Berotralstat

Betrixaban

Bictegravir

Carbamazepine

Cariprazine

Cenobamate

Ceritinib

Chlorpheniramine

Cisatracurium

Clarithromycin

Clofazimine

Clozapine

Cobimetinib

Codeine

Copanlisib

Crizotinib

Cyclophosphamide

Dabigatran Etexilate

Dabrafenib

Daridorexant

Darolutamide

Dasatinib

Deferasirox

Deflazacort

Desogestrel

Dexamethasone

Diazepam

Diazoxide

Dienogest

Digoxin

Dihydrocodeine

Dihydroxyaluminum Aminoacetate

Dihydroxyaluminum Sodium Carbonate

Dolutegravir

Doxifluridine

Doxorubicin

Doxorubicin Hydrochloride Liposome

Dronedarone

Drospirenone

Duvelisib

Edoxaban

Elacestrant

Elexacaftor

Eliglustat

Encorafenib

Entrectinib

Enzalutamide

Eravacycline

Erdafitinib

Erlotinib

Eslicarbazepine Acetate

Estetrol

Estradiol

Ethinyl Estradiol

Ethosuximide

Ethynodiol

Etonogestrel

Etravirine

Everolimus

Exemestane

Ezogabine

Fedratinib

Fenfluramine

Fentanyl

Fexinidazole

Finerenone

Fluconazole

Fluorouracil

Fluoxetine

Fluvastatin

Fosaprepitant

Fosnetupitant

Fostamatinib

Futibatinib

Gefitinib

Gepirone

Gestodene

Gilteritinib

Glasdegib

Glecaprevir

Halothane

Hemin

Hydrocodone

Ibrexafungerp

Ibrutinib

Idelalisib

Ifosfamide

Imatinib

Infigratinib

Infliximab

Irinotecan

Irinotecan Liposome

Istradefylline

Itraconazole

Ivabradine

Ivacaftor

Ivosidenib

Ixabepilone

Ixazomib

Ketoconazole

Lamotrigine

Lapatinib

Larotrectinib

Ledipasvir

Lefamulin

Lemborexant

Leniolisib

Letermovir

Levoketoconazole

Levoleucovorin

Levonorgestrel

Lidocaine

Linagliptin

Lopinavir

Lumateperone

Lurbinectedin

Macimorelin

Macitentan

Magaldrate

Magnesium Carbonate

Magnesium Hydroxide

Magnesium Oxide

Magnesium Trisilicate

Manidipine

Maribavir

Medroxyprogesterone

Meperidine

Mestranol

Methadone

Methotrexate

Methylphenidate

Metronidazole

Miconazole

Midostaurin

Mifepristone

Mirtazapine

Mitapivat

Mobocertinib

Naloxegol

Neratinib

Netupitant

Nifedipine

Nilotinib

Nimodipine

Nintedanib

Nitisinone

Nomegestrol

Norelgestromin

Norethindrone

Norgestimate

Norgestrel

Olanzapine

Olaparib

Olutasidenib

Omaveloxolone

Omeprazole

Orlistat

Osimertinib

Oxcarbazepine

Oxycodone

Paclitaxel

Palbociclib

Paliperidone

Palovarotene

Panobinostat

Pazopanib

Pemigatinib

Pentazocine

Perampanel

Pexidartinib

Phenobarbital

Pibrentasvir

Pimavanserin

Pirtobrutinib

Pitolisant

Ponatinib

Ponesimod

Posaconazole

Pralsetinib

Pretomanid

Primidone

Quetiapine

Quizartinib

Regorafenib

Relugolix

Reserpine

Ribociclib

Rifampin

Rimegepant

Ripretinib

Risperidone

Ritlecitinib

Rivaroxaban

Rocuronium

Roflumilast

Rolapitant

Romidepsin

Ruxolitinib

Samidorphan

Saquinavir

Segesterone

Selpercatinib

Selumetinib

Sertraline

Sildenafil

Simeprevir

Sirolimus Protein-Bound

Sofosbuvir

Sonidegib

Sorafenib

Sotorasib

Sparsentan

Stiripentol

St John's Wort

Sufentanil

Sulfamethoxazole

Sunitinib

Tacrolimus

Tamoxifen

Tasimelteon

Tazemetostat

Tegafur

Temsirolimus

Tezacaftor

Theophylline

Thiotepa

Ticagrelor

Tivozanib

Tocilizumab

Tofacitinib

Tolvaptan

Topiramate

Trabectedin

Tramadol

Triclabendazole

Trimethoprim

Tucatinib

Ubrogepant

Ulipristal

Upadacitinib

Valbenazine

Valproic Acid

Vandetanib

Velpatasvir

Vemurafenib

Venetoclax

Vilazodone

Vincristine

Vincristine Sulfate Liposome

Vinflunine

Voclosporin

Vonoprazan

Vorapaxar

Voriconazole

Vortioxetine

Voxelotor

Voxilaprevir

Zanubrutinib

Zolpidem

Zuranolone

Using this medicine 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.

Acetaminophen

Acetazolamide

Acyclovir

Amitriptyline

Amprenavir

Aripiprazole Lauroxil

Atorvastatin

Betamethasone

Bexarotene

Bleomycin

Busulfan

Carboplatin

Caspofungin

Chloramphenicol

Cimetidine

Ciprofloxacin

Cisplatin

Clobazam

Clopidogrel

Colesevelam

Cortisone

Cyclosporine

Dicumarol

Digitoxin

Diltiazem

Disopyramide

Disulfiram

Doxepin

Felbamate

Fludrocortisone

Fluvoxamine

Folic Acid

Fosamprenavir

Ginkgo

Imipramine

Isoniazid

Levodopa

Levofloxacin

Levomethadyl

Levothyroxine

Lithium

Methoxsalen

Methsuximide

Midazolam

Nafimidone

Nelfinavir

Nilutamide

Nisoldipine

Ospemifene

Pancuronium

Paroxetine

Phenprocoumon

Piperine

Prednisolone

Prednisone

Progabide

Quinidine

Quinine

Remacemide

Rifapentine

Rufinamide

Sabeluzole

Semaglutide

Shankhapulshpi

Simvastatin

Sirolimus

Sulfamethizole

Sulfaphenazole

Sulthiame

Telithromycin

Tenidap

Tiagabine

Ticlopidine

Ticrynafen

Tirilazad

Tizanidine

Tolbutamide

Trazodone

Triamcinolone

Tubocurarine

Valacyclovir

Vecuronium

Verapamil

Vigabatrin

Viloxazine

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 this medicine 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 this medicine, or give you special instructions about the use of food, alcohol, or tobacco.

Enteral Nutrition

Ethanol

How to use Phenytoin (Oral)

Take this medicine only as directed by your doctor. Do not take more of it, do not take it more often, and do not take it for a longer time than your doctor ordered.

This medicine should come with a Medication Guide. Read and follow these instructions carefully. Ask your doctor if you have any questions.

This medicine may be used with other seizure medicines. Keep using all of your seizure medicines unless your doctor tells you otherwise.

Do not change brands or dosage forms of phenytoin without first checking with your doctor. Different products may not work the same way. If you refill your medicine and it looks different, check with your pharmacist.

Swallow the tablet whole or chew it thoroughly before swallowing it together with a glass of water.

Measure the oral suspension with a marked measuring spoon, oral syringe, or medicine cup. Rinse the dosing spoon or cup with water after each use.

If you are receiving tube feeding preparations, it is best to take this medicine before or after a feeding.

Dosing

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.

Missed Dose

If you miss a dose of this medicine, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.

Storage

Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Keep from freezing.

Keep out of the reach of children.

Do not keep outdated medicine or medicine no longer needed.

Ask your healthcare professional how you should dispose of any medicine you do not use.

Warnings

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 suddenly stop using this medicine without checking first with your doctor. Stopping the medicine suddenly may cause your seizures to return or to occur more often. Your doctor may want you or your child to gradually reduce the amount you are using before stopping it completely.

This medicine may cause serious allergic reactions, including angioedema, which can be life-threatening and require immediate medical attention. Tell your doctor right away if you or your child have large, hive-like swelling on the face, eyelids, lips, tongue, throat, hands, legs, feet, or sex organs after using this medicine.

Serious skin reactions (eg, Stevens-Johnson syndrome, toxic epidermal necrolysis, and acute generalized exanthematous pustulosis) can occur while using this medicine. Check with your doctor right away if you have blistering, peeling, or loosening of the skin, chills, cough, diarrhea, itching, joint or muscle pain, red irritated eyes, red skin lesions, often with a purple center, sore throat, sores, ulcers, or white spots in the mouth or on the lips, or unusual tiredness or weakness with 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 problems. 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 the density of bones, which can make your bones weak. Talk with your doctor if you have any concerns about this.

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. Make sure the doctor knows if you have trouble sleeping, get upset easily, have a big increase in energy, or start to act reckless. Also tell the doctor if you have sudden or strong feelings, such as feeling nervous, angry, restless, violent, or scared. If you, your child, or your caregiver notice any of these side effects, tell your 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. Make sure you know how you or your child react to this medicine before you drive, use machines, climb in high places, swim, or do anything else that could be dangerous if you are not alert, well-coordinated, or able to think or see well.

Avoid drinking alcohol while you are using this medicine.

Using this medicine together with valproate (Depacon®, Depakene®) may increase the risk of having hyperammonemia (too much ammonia in your blood), which may damage the brain and can be life-threatening. Check with your doctor right away if you or your child have nausea or vomiting that continues, an increase in the frequency of seizures, loss of appetite, swelling of the face, tiredness and weakness, or yellow eyes or skin.

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.

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