Description and Brand Names

Drug information provided by: Merative, Micromedex®

Descriptions

Phenytoin injection is used to control certain types of seizures (convulsions) 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 to be given only or under the direct supervision of a doctor.

This product is available in the following dosage forms:

• Solution

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 injection in children.

Geriatric

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

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 receiving 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
• 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
• 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
• Dolutegravir
• Dopamine
• 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
• 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
• 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.

• Ethanol

Other Medical Problems

The presence of other medical problems may affect the use of this medicine. Make sure you tell your doctor if you have any other medical problems, especially:

• Blood or bone marrow problems (eg, agranulocytosis, leukopenia, thrombocytopenia) or
• Diabetes or
• Heart failure or
• Heart rhythm problems or
• Hypotension (low blood pressure) or
• Lymphadenopathy (lymph node problems) or
• Porphyria (an enzyme problem)—Use with caution. May make these conditions worse.

• Heart block (eg, Adams-Stokes syndrome, AV block, or sinoatrial block) or
• Sinus bradycardia (slow heartbeat)—Should not be used in patients with these conditions.

• Hypoalbuminemia (low albumin in the blood) or
• Kidney disease or
• Liver disease—Use with caution. The effects may be increased because of slower removal from the body.

Proper Use

A nurse or other trained health professional will give you or your child this medicine in a hospital. This medicine is given as a shot into a muscle or into a vein.

Your doctor will only give you or your child a few doses of this medicine until your condition improves. You will be switched to an oral medicine that works the same way. If you have any concerns about this, talk to your doctor.

Precautions

It is very important that your doctor check your progress closely while you or your child are receiving this medicine. This is to see if it is working properly and to allow for a change in the dose. Blood 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 receive this medicine while you or your child are also taking delavirdine (Rescriptor®). Using these medicines together may cause unwanted effects.

This medicine may cause some people to become dizzy, lightheaded, faint, or less alert than they are normally. Make sure you know how you react to this medicine before you drive, use machines, or do anything else that could be dangerous if you are dizzy or are not alert and able to see well.

Do not stop using this medicine without first checking with your doctor. Stopping the medicine suddenly may cause your seizures to return or to occur more often.

If you or your child develop a skin rash, hives, or any allergic reaction to this medicine, tell your doctor or nurse as soon as possible.

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 receiving this medicine. These may be symptoms of a serious and life-threatening condition called Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS).

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.

This medicine may cause purple glove syndrome. Tell your doctor right away if you or your child have skin discoloration, pain, or swelling at the injection site after receiving this medicine.

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.

If you or your child develop any unusual or strange thoughts and behavior while receiving phenytoin injection, be sure to discuss it with your doctor. Some changes that have occurred in people receiving this medicine are like those seen in people who drink too much alcohol. Other changes might be confusion, worsening of depression, hallucinations (seeing, hearing, or feeling things that are not there), suicidal thoughts, and unusual excitement, nervousness, or irritability.

Birth control pills may not work while you are using this medicine. To keep from getting pregnant, use another form of birth control along with your birth control pills. Other forms include a condom, a diaphragm, or a contraceptive foam or jelly.

Avoid drinking alcohol while you are receiving this medicine.

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.

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 or nurse immediately if any of the following side effects occur:

More common

1. Chest pain or discomfort
2. cold, clammy, or pale skin
3. decreased coordination
4. difficulty with sleeping
5. disorientation
6. dizziness
7. drowsiness to profound coma
8. fainting
9. fast, slow, or irregular heartbeat
10. hallucination
11. headache
12. lightheadedness
13. measles-like skin rash
14. mood or other mental changes
15. nausea
16. nervousness
17. pain in the shoulders, back, neck, or jaw
18. shakiness and unsteady walk
19. slow heart rate
20. slurred speech
21. sweating
22. swelling of the feet and lower legs
23. troubled breathing
24. uncontrolled eye movements
25. unsteadiness, trembling, or other problems with muscle control or coordination
26. unusual tiredness or weakness

Rare

1. Bleeding, blistering, burning, coldness, discoloration of the skin, feeling of pressure, hives, infection, inflammation, itching, lumps, numbness, pain, rash, redness, scarring, soreness, stinging, swelling, tenderness, tingling, ulceration, or warmth at the injection site
2. blistering, crusting, irritation, itching, peeling, or reddening of the skin
3. cracked, dry, or scaly skin
4. inability to move the eyes
5. increased blinking or spasms of the eyelid
6. shakiness in the legs, arms, hands, or feet
7. sticking out of the tongue
8. trouble with breathing, speaking, or swallowing
9. twitching, uncontrolled movements of the tongue, lips, face, neck, trunk, arms, or legs
10. unusual facial expressions

Incidence not known

1. Abdominal or stomach pain
2. bleeding gums
3. blisters, hives, or itching
4. bloating of the abdomen or stomach
5. blood in the urine or stools
6. bloody, black, or tarry stools
7. blurred vision
8. break in the skin, especially associated with blue-black discoloration, swelling, or drainage of fluid
9. burning, numbness, tingling, or painful sensations
10. chills
11. cough or hoarseness
12. dark urine
13. diarrhea
14. dizziness, faintness, or lightheadedness when getting up suddenly from a lying or sitting position
15. fainting spells
16. fever with or without chills
17. general feeling of discomfort or illness
18. general feeling of tiredness or weakness
19. hair loss
20. high fever
21. irritation in the mouth
22. joint or muscle pain
23. light-colored stools
24. loss of appetite
25. loss of heat from the body
26. lower back or side pain
27. muscle or joint pain
28. painful or difficult urination
29. pale skin
30. pinpoint red spots on the skin
31. red skin lesions, often with a purple center
32. red, irritated eyes
33. red, swollen skin
34. redness and swelling of the gums
35. skin rash
36. sore throat
37. soreness of the muscles
38. sores, ulcers, or white spots on the lips or in the mouth
39. stomach pain, continuing
40. sweating
41. swollen glands
42. swollen, painful, or tender lymph glands in the neck, armpit, or groin
43. unexplained bleeding or bruising
44. unsteadiness or awkwardness
45. unusual bleeding or bruising
46. vomiting
47. weakness in the arms, hands, legs, or feet
48. weight loss
49. yellow eyes or skin

Get emergency help immediately if any of the following symptoms of overdose occur:

Symptoms of overdose

1. Change in consciousness
2. changes in patterns and rhythms of speech
3. loss of consciousness
4. pounding in the ears
5. unusual drowsiness, dullness, tiredness, weakness, or feeling of sluggishness

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:

Incidence not known

1. Difficulty having a bowel movement (stool)
2. enlarged lips
3. feeling of constant movement of self or surroundings
4. increased hair growth on the forehead, back, arms, and legs
5. pain of the penis on erection
6. 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-injection-route/side-effects/drg-20072593