Phenytoin (Oral Route) Before Using

Description and Brand Names

Drug information provided by: Merative, Micromedex®

US Brand Name

Dilantin
Dilantin-125
Dilantin Infatabs
Phenytek

Canadian Brand Name

Dilantin-30

Descriptions

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.

This product is available in the following dosage forms:

Tablet, Chewable
Suspension
Capsule, Extended Release

Before Using

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.

Breastfeeding

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.

Drug Interactions

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 Sulfate
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
Bortezomib
Bosutinib
Brexpiprazole
Brigatinib
Buprenorphine
Bupropion
Cabozantinib
Calcifediol
Calcium Carbonate
Cannabidiol
Capecitabine
Capivasertib
Capmatinib
Carbamazepine
Cariprazine
Cenobamate
Ceritinib
Chlorpheniramine
Cisatracurium
Clarithromycin
Clofazimine
Clozapine
Cobimetinib
Codeine
Copanlisib
Crizotinib
Cyclophosphamide
Cyclosporine
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
Enasidenib
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
Fruquintinib
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
Nirogacestat
Nitisinone
Nomegestrol
Norelgestromin
Norethindrone
Norgestimate
Norgestrel
Olanzapine
Olaparib
Oliceridine
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
Repotrectinib
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
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
Rufinamide
Sabeluzole
Shankhapulshpi
Simvastatin
Sirolimus
Sulfamethizole
Sulfaphenazole
Sulthiame
Telithromycin
Tenidap
Tiagabine
Ticlopidine
Ticrynafen
Tirilazad
Tizanidine
Tolbutamide
Trazodone
Triamcinolone
Tubocurarine
Valacyclovir
Vecuronium
Verapamil
Vigabatrin
Viloxazine

Other Interactions

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

Proper Use

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.
  - 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.

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.

Precautions

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.

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.

Portions of this document last updated: April 01, 2024

Original article: https://www.mayoclinic.org/drugs-supplements/phenytoin-oral-route/before-using/DRG-20072875

Phenytoin (Oral Route)

Description and Brand Names

US Brand Name

Canadian Brand Name

Descriptions

Before Using

Allergies

Pediatric

Geriatric

Breastfeeding

Drug Interactions

Other Interactions

Other Medical Problems

Proper Use

Dosing

Missed Dose

Storage

Precautions

Side Effects

More common

Rare

Incidence not known

More common

Incidence not known

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