Phenytoin (Injection)

Phenytoin is an injected medication utilized by physicians to prevent seizure conditions in the brain as the result of epilepsy or cranial surgery.


Phenytoin is also known under the trade name of Dilantin in medical circles and is a versatile anticonvulsant, anti-epileptic medication injected by doctors to combat seizures in the brain that happen in epileptic patients or patients who have had recent neurosurgical procedures. Phenytoin is used to control the seizure by slowing down the brain's impulses; it is also a muscle relaxant, but rarely used for this purpose.

Phenytoin is not effective on all seizure types and its use must be determined to be appropriate by your physician.

Phenytoin affects an area of the brain known as the motor cortex of the brain, which controls both voluntary and involuntary movement. Phenytoin works to stop the seizure activity from spreading, reducing the chance of the seizure becoming full blown, also known as grand mal.

Phenytoin halts the involuntary energy conduction activity in the brain cells of a patient having a seizure. By traveling through the neuron cell membranes, Phenytoin dampens the abnormal energy synapses, which normalizes the activity and calms the seizures.

Epilepsy is a brain condition that gives the patient seizures on a semi-regular basis. All brain activity is electrical, consisting of cellular communication back and forth. When a person has a seizure, it is the result of an explosion of electrical activity in the brain cells, which temporarily disrupt normal function.

The part of the brain affected by the abnormal burst of energy determines the type of seizure a person has. Not all seizures are epileptic in nature and not all seizures are controlled with Phenytoin.

Phenytoin treats seizures that are partial in nature and those referred to as tonic-clonic. Partial seizures affect only one of the two hemispheres or only one of the four lobes in the brain. Tonic-colonic used to be referred to as a grand mal seizure that affects the entire brain. This is the type of seizure that is typically associated with the epilepsy condition.

Conditions Treated

Type Of Medicine

  • Antiepileptic
  • Antiseizure

Side Effects

Phenytoin directly affects brain activity at the cellular level, in the motor cortex portion of the brain. It is a very powerful drug and, due to the way it works, may cause adverse health effects that can require urgent medical attention. Notify your physician or medical staff if you exhibit any of the following symptoms:

  • Pale, clammy, cold skin
  • Lack of muscle coordination
  • Pain in the chest
  • Insomnia
  • Disoriented demeanor
  • Dizzy
  • Drowsy to the extreme
  • Fainting or lightheadedness
  • Irregular heart rhythm
  • Hallucinations
  • Headache
  • Skin rash representing measles
  • Mental or mood changes
  • Nausea
  • Nervous demeanor
  • Pain in the jaw, neck, back or shoulders
  • Shaking
  • Walking unsteadily
  • Sluggish heart rhythm
  • Speech changes including slurring
  • Difficulty breathing
  • Sweating
  • Swollen lower legs or feet
  • Spastic eye movements
  • Trembling
  • Muscle coordination or control problems
  • Fatigue
  • Weak muscles
  • Injection site abnormalities in texture, color or temperature
  • Signs of skin infection
  • Skin irritation, peeling or itchy, crusty skin
  • Skin is scaly or dry and cracked
  • Unable to move eyes
  • Eyelid spasms
  • Constant blinking
  • Sticking out tongue constantly
  • Shaky muscles or limbs
  • Difficulty speaking, swallowing or breathing
  • Twitchy, out-of-control movements of the body, legs, arms, face or tongue
  • Strange facial expressions
  • Abdominal pain
  • Gums bleeding
  • Itchy, blistered skin with hives
  • Bloated stomach or abdomen
  • Blood in stools or urine
  • Stools appear black or tar-like
  • Vision is blurry
  • Broken, bruised skin
  • Swollen, draining skin lesions
  • Chills
  • Pain, numbness, tingling or burning sensations
  • Hoarse voice or coughing
  • Urine that is dark in color
  • Diarrhea
  • Fainting, feeling lightheaded after rising or being dizzy
  • Spells of passing out
  • Fever and possible chills
  • Overall unwell feeling
  • Uncomfortable
  • Weak feeling
  • Tired feeling
  • Loss of hair
  • Elevated temperature
  • Mouth sores or irritation
  • Pain in joints or muscles
  • Stools appear light in color
  • No appetite
  • Cannot retain body heat
  • Pain in side or lower back
  • Urination is difficult or painful
  • Skin is pale
  • Skin shows tiny red dots
  • Skin shows red dots with purple centers
  • Eyes are blood shot and irritated
  • Skin is swollen or red
  • Gums are swollen or red
  • Rash on skin
  • Throat soreness
  • Muscle pain
  • White ulcerated sores in the mouth or on the lips
  • Constant pain in stomach
  • Sweating
  • Glands are swollen, tender or painful in armpit, neck or groin
  • Unexpected bruising or bleeding that can't be explained
  • Awkward, unsteady demeanor
  • Vomiting
  • Weak limbs or extremities
  • Loss of weight
  • Yellow tinge to eyes or skin

Overdose of this medication may give the following symptoms, which should prompt you to seek emergency medical treatment:

  • Change or loss of consciousness
  • Speech rhythm or pattern changes
  • Ear pounding
  • Dull, tired, sluggish feeling
  • Extreme fatigue
  • Extreme muscle weakness

Other health effects, while annoying, are typically temporary in nature and will go away with time as your body gets used to Phenytoin. Your health care provider will be able to advise you on ways to lessen or eliminate these symptoms:

  • Constipation
  • Swollen lips
  • Spinning or constant motion feeling
  • Unusual hair growth on arms, back, legs or forehead
  • Painful erection

Other health effects may occur after you have been treated with Phenytoin than what are listed here. Any changes to your overall health, wellbeing or demeanor should be reported to your medical professional team right away.


The injected form of Phenytoin is given to you by a trained medical professional such as a doctor, nurse, surgeon or other appropriate staff. This medication is for temporary seizure relief only; you will be receiving a prescription to an oral medication with similar control effects for everyday use. Make sure you understand all information provided to you in the printed leaflet that arrives with your prescription, asking questions for clarity when needed.

In emergency seizure situations, Phenytoin injection, if administered too quickly, can cause cardiac episodes that are life-threatening. Intravenous administration of this drug, therefore, should not exceed 50 milligrams per minute in adult patients. Pediatric patients will typically be given Phenytoin at a rate of one to three milligrams per kilogram of body weight per minute or 50 milligrams per minute, using the slower dosage of the two.

For non-emergency injections, a loading dose will typically be given followed by intermittent doses until the patient's seizures are under control and their condition is stabilized. The loading dose is typically injected slowly, again not exceeding 50 milligrams per minute for adult patients and one to three milligrams per kilogram of body weight or 50 milligrams per minute, choosing the slower of the two for pediatric patients.

In epileptic patients, an initial or loading dose will typically consist of ten to fifteen milligrams per kilogram of body weight that will be bolstered by maintenance oral medication after the initial dose has done its work. Pediatric epileptic patients will have an initial dose of fifteen to twenty milligrams per kilogram of body weight. For all patients, the 50 milligrams per minute limit must be adhered to for safety and monitoring of cardiac activity including blood pressure will continue throughout the dosage.


Hypersensitivity to other medications, certain foods, animals, artificial additives and dyes should be communicated to your health care provider to avoid any unwanted reactions to Phenytoin. Inform your health care provider if you are taking any other medications including over the counter medicines, herbal therapies, vitamins or holistic remedies. As this drug will most likely be administered to you in an emergency situation, make sure that your medical history is up to date on your latest drug treatments so that it can be referred to for possible interactions

All drug therapies come with risk factors that will be explained to you by your physician. You will also be given a patient leaflet that you should read completely. Ask questions about any information contained in this leaflet that you don't understand.

Some medications are able to be used together without harm or reduced effectiveness of either drug. Combination therapies are a way to combat symptoms and make the patient more able to live a normal life. However, there are some drugs that should not be combined. The following medications should never be administered while you are being treated with Phenytoin:

  • Artemether
  • Amifampridine
  • Boceprevir
  • Atazanavir
  • Daclatasvir
  • Cobicistat
  • Dasabuvir
  • Darunavir
  • Delavirdine
  • Delamanid
  • Elvitegravir
  • Elbasvir
  • Isavuconazonium
  • Grazoprevir
  • Maraviroc
  • Lurasidone
  • Paritaprevir
  • Ombitasvir
  • Praziquantel
  • Piperaquine
  • Rilpivirine
  • Ranolazine
  • Telaprevir
  • Ritonavir

The following medications are known to have adverse reactions with Phenytoin, but may be critical to your health care. Make sure you physician knows if you take any of the following substances so that dosage amounts can be appropriately altered for safety and effectiveness:

  • Abiraterone
  • Apazone
  • Afatinib
  • Apremilast
  • Apixaban
  • Aripiprazole
  • Aprepitant
  • Beclamide
  • Axitinib
  • Blinatumomab
  • Bedaquiline
  • Bosutinib
  • Bortezomib
  • Bupropion
  • Brexpiprazole
  • Calcifediol
  • Cabozantinib
  • Cariprazine
  • Carbamazepine
  • Clarithromycin
  • Ceritinib
  • Cobimetinib
  • Clozapine
  • Cyclophosphamide
  • Crizotinib
  • Dabrafenib
  • Dabigatran Etexilate
  • Deferasirox
  • Dasatinib
  • Diazoxide
  • Diazepam
  • Dolutegravir
  • Digoxin
  • Doxorubicin
  • Dopamine
  • Dronedarone
  • Doxorubicin Hydrochloride Liposome
  • Enzalutamide
  • Eliglustat
  • Eslicarbazepine Acetate
  • Erlotinib
  • Etravirine
  • Ethosuximide
  • Exemestane
  • Everolimus
  • Fentanyl
  • Ezogabine
  • Fosaprepitant
  • Fluvastatin
  • Golimumab
  • Gefitinib
  • Hydrocodone
  • Halothane
  • Idelalisib
  • Ibrutinib
  • Imatinib
  • Ifosfamide
  • Irinotecan
  • Infliximab
  • Itraconazole
  • Irinotecan Liposome
  • Ivacaftor
  • Ivabradine
  • Ixazomib
  • Ixabepilone
  • Lapatinib
  • Ketoconazole
  • Lidocaine
  • Ledipasvir
  • Lopinavir
  • Linagliptin
  • Manidipine
  • Macitentan
  • Miconazole
  • Methotrexate
  • Naloxegol
  • Mifepristone
  • Nifedipine
  • Netupitant
  • Nimodipine
  • Nilotinib
  • Olaparib
  • Nintedanib
  • Osimertinib
  • Orlistat
  • Palbociclib
  • Oxycodone
  • Pazopanib
  • Panobinostat
  • Pixantrone
  • Perampanel
  • Posaconazole
  • Ponatinib
  • Regorafenib
  • Quetiapine
  • Rifampin
  • Reserpine
  • Rocuronium
  • Rivaroxaban
  • Rolapitant
  • Roflumilast
  • Saquinavir
  • Romidepsin
  • Sertraline
  • Secukinumab
  • Simeprevir
  • Siltuximab
  • Sonidegib
  • Sofosbuvir
  • St John's Wort
  • Sorafenib
  • Tacrolimus
  • Sunitinib
  • Tasimelteon
  • Tamoxifen
  • Tenofovir Alafenamide
  • Temsirolimus
  • Thiotepa
  • Theophylline
  • Tofacitinib
  • Ticagrelor
  • Trabectedin
  • Tolvaptan
  • Vandetanib
  • Ulipristal
  • Vemurafenib
  • Velpatasvir
  • Vilazodone
  • Venetoclax
  • Vincristine Sulfate Liposome
  • Vincristine
  • Vorapaxar
  • Vinflunine
  • Vortioxetine
  • Voriconazole

The following drugs, while they may increase unwanted health effects with use of Phenytoin, may be necessary to your health care as well. Let you physician know if you are taking:

  • Acetazolamide
  • Acetaminophen
  • Amiodarone
  • Acyclovir
  • Amprenavir
  • Amitriptyline
  • Betamethasone
  • Atorvastatin
  • Bleomycin
  • Bexarotene
  • Capecitabine
  • Busulfan
  • Caspofungin
  • Carboplatin
  • Cimetidine
  • Chloramphenicol
  • Cisplatin
  • Ciprofloxacin
  • Clofazimine
  • Clobazam
  • Cortisone
  • Clopidogrel
  • Desogestrel
  • Cyclosporine
  • Dicumarol
  • Dexamethasone
  • Digitoxin
  • Dienogest
  • Disopyramide
  • Diltiazem
  • Doxepin
  • Disulfiram
  • Drospirenone
  • Doxifluridine
  • Estradiol Valerate
  • Estradiol Cypionate
  • Ethynodiol Diacetate
  • Ethinyl Estradiol
  • Felbamate
  • Etonogestrel
  • Fludrocortisone
  • Fluconazole
  • Fluoxetine
  • Fluorouracil
  • Folic Acid
  • Fluvoxamine
  • Ginkgo
  • Fosamprenavir
  • Isoniazid
  • Imipramine
  • Levomethadyl
  • Levodopa
  • Levothyroxine
  • Levonorgestrel
  • Meperidine
  • Medroxyprogesterone Acetate
  • Methoxsalen
  • Mestranol
  • Midazolam
  • Methsuximide
  • Nelfinavir
  • Nafimidone
  • Nisoldipine
  • Nilutamide
  • Norethindrone
  • Norelgestromin
  • Norgestrel
  • Norgestimate
  • Oxcarbazepine
  • Ospemifene
  • Pancuronium
  • Paclitaxel
  • Phenprocoumon
  • Paroxetine
  • Prednisolone
  • Piperine
  • Progabide
  • Prednisone
  • Quinine
  • Quinidine
  • Rifapentine
  • Remacemide
  • Rufinamide
  • Risperidone
  • Shankhapulshpi
  • Sabeluzole
  • Sirolimus
  • Simvastatin
  • Sulfamethoxazole
  • Sulfamethizole
  • Sulthiame
  • Sulfaphenazole
  • Telithromycin
  • Tegafur
  • Tiagabine
  • Tenidap
  • Ticrynafen
  • Ticlopidine
  • Tizanidine
  • Tirilazad
  • Topiramate
  • Tolbutamide
  • Triamcinolone
  • Trazodone
  • Tubocurarine
  • Trimethoprim
  • Valproic Acid
  • Valacyclovir
  • Verapamil
  • Vecuronium
  • Viloxazine
  • Vigabatrin

Consult with your physician on whether to eat prior or during your treatment with Phenytoin or whether some foods should be eliminated from your diet altogether. You should also inform your doctor if you are a regular user of tobacco products or alcoholic beverages, as these could affect the way Phenytoin works for you. It is not advised that you consume anything ethanol alcohol while taking Phenytoin.

Your full medical history should be communicated to your physician in case you have diseases that would be dangerously affected by chemotherapy treatment such as Phenytoin. Specifically, the following health conditions have been known to become worse or limit the effectiveness of this medication:

  • Blood diseases
  • Bone marrow diseases
  • Diabetes
  • Heart rate issues
  • Cardiac failure
  • Low blood pressure
  • Lymph node problems
  • Enzyme issues
  • Heart blockage
  • Slow heart rhythm
  • Low blood albumin levels
  • Disease of the kidneys
  • Disease of the liver


Your health condition will be closely monitored while you are being treated with Phenytoin to make sure it is effective on your condition and that you aren't suffering from any adverse symptoms. Blood sample testing may be involved in this monitoring process.

Phenytoin has been known to pose a risk to unborn children and should not be used in women who are pregnant or who may become pregnant. An effective birth control method is advised for use in women being treated with this medication. If you become pregnant while being treated with Phenytoin, inform your physician as soon as you suspect your condition.

Data from studies on women who are breastfeeding has not been provided with any level of confidence that determines a risk to children and infants as far as transmission of Phenytoin through breast milk. Use of this medication on women who are nursing should be determined with regard to their health needs and the health of their children.

No data has been provided from studies on pediatric or geriatric patients with regard to the effectiveness of Phenytoin or with regard to increased risks. It is believed to be appropriate for these age groups, with the caution that geriatric patients may have kidney, heart or liver problems that may create an increased risk for them.

Delvirdine, also marketed as Rescriptor, is a medication that should not be used with Phenytoin treatment as the health effects the two drugs would cause together would pose a danger to your health. Make sure your medical professionals know if you are taking Delvirdine.

Some patients become lightheaded, pass out or are dizzy and less alert than they normally are. For this reason, driving, operating heavy machinery or power tools should not be done while you are on this medication.

Be alert for signs of Drug Reaction with Eosinophilia and Systemic Symptoms condition or DRESS with use of Phenytoin, which includes:

  • Swollen lymph glands located in the grin, neck or armpit
  • Bruising or bleeding that is unusual or unexpected
  • Fever
  • Skin rash
  • Yellow skin or eyes

Phenytoin puts patients at risk for damage to their liver. Signs of damage include yellow tinge to eyes or skin, dark colored urine, little to no appetite, nausea and vomiting or pain in the stomach area. Alert your medical professional if you show any of these symptoms.

You may be at a higher risk for a skin condition known as PGS, which can have long-term serious implications on your health. Also known as purple glove syndrome, PGS can be indicated by signs of discoloration, swelling or pain at the site of the injection of Phenytoin. Let your health care professional know if your injection site appears strange in any way.

Blood sugar levels can be affected with use of Phenytoin and diabetic patients should especially be monitored for glucose levels. Your doctor will need to know if you are diabetic or pre-diabetic if you have been given an injection of Phenytoin.

Patients who exhibit strange behavior patterns or who are having abnormal thought processes after an injection of Phenytoin should discuss these symptoms with their doctors right away. Patients who consume alcoholic beverages are at a higher risk for these symptoms, which include depression, hallucinating, confusion, suicidal thoughts, nervousness, irritable mood or excitability. Discuss these behavior and mood changes with your health care provider.

Your birth control pills may not be effective if you have been treated with injections of Phenytoin, so it is advised that you utilize other birth control methods during your treatment with this medication. Discuss your birth control options with your health care provider.

Avoid consuming alcoholic beverages while you are being treated with Phenytoin. Seek assistance if you require it during this time.

Other doctors and dentists giving you procedures or tests after you have been given Phenytoin injection may not see results they are expecting. Be sure to communicate the fact that you have been treated with this drug to other physicians when applicable.

Many medications, vitamins and mineral supplements interact adversely with Phenytoin. Avoid taking any other medications while you are being treated with this drug, including over-the-counter, herbal, and holistic or vitamin supplements.


Phenytoin will be stored and administered in a hospital or cancer center setting only, with storage according to the manufacturer's instructions carried out by the professional staff. This medication is provided by the manufacturer in single dose packages that should be used once opened or discarded immediately if not used. Room temperature storage is recommended with cautions not to expose the packaging to heat, light, moisture or freezing.


Phenytoin is an injected antiseizure drug administered during emergency situations or surgical settings to calm inappropriate brain electrical wave activity. Phenytoin is sold under the trade name Dilantin and other names and works on partial seizures of the brain as well as tonic-clonic seizures. Tonic-clonic seizures are mostly associated with epileptic condition in patients.

Phenytoin works by blocking certain channels in the brain that exist in the motor cortex, the central portion of the brain. When the electrical activity that the brain cells use to communicate becomes extremely hyperactive, this causes a seizure. Phenytoin steps in to calm this unusual activity and thereby stop the seizure from happening.

Phenytoin is only for the temporary use of medical professionals and dosage safety, storage conditions and other considerations are up to the staff following manufacturer's instructions. After a patient's condition is stabilized with Phenytoin, an oral medication will most likely be prescribed to continue controlling the condition of the patient going forward.

Unwanted health effects include drowsiness, confused demeanor, nervousness, nausea, constipation, skin rash, uncontrollable ocular movement, headaches and insomnia. Serious problems should be reported to your doctor right away. Severe conditions that occur as the result of Phenytoin include PGS, which is an infection of the site of the injection as well as irrational behavior or altered mood. Liver damage as well as DRESS syndrome are also at a particularly high risk for patients on this medication. Any changes to your overall health, mood or wellbeing should be reported to your medical team right away.

Patients are instructed not to consume alcoholic beverages while being treated with Phenytoin. Patients should also avoid taking any other medications with this drug, whether they are prescription or non-prescription, as the list of interactivity that causes adverse health effects is extensive. Patients may be at risk for heart failure if this drug is administered too quickly. Patients are also at risk if they have liver or kidney diseases or if they are diabetic. Make sure your full medical history is available to your doctor should you require treatment with Phenytoin.

Most patients are able to benefit from the effects of Phenytoin, should they need emergency brain seizure treatment. Women who are pregnant or who are nursing should avoid this treatment unless it is an emergency, as it can pose a risk to their unborn children or infants. Geriatric patients who have kidney, liver or cardiac diseases should also be administered Phenytoin with caution.

Last Reviewed:
March 26, 2018
Last Updated:
April 03, 2018