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Phenytoin is an anti-epileptic drug, also called an anticonvulsant. Phenytoin works by slowing down impulses in the brain that cause seizures.
Phenytoin is used to control seizures. It does not treat all types of seizures, and your doctor will determine if it is the right medicine for you.
You should not use phenytoin if you also take delavirdine (Rescriptor), or if you are allergic to ethotoin (Peganone), fosphenytoin (Cerebyx), or mephenytoin (Mesantoin). If you are pregnant, DO NOT START TAKING this medicine unless your doctor tells you to. Phenytoin may cause harm to an unborn baby, but having a seizure during pregnancy could harm both the mother and the baby. If you become pregnant while taking this medicine, DO NOT STOP TAKING the medicine without your doctor's advice. Seizure control is very important during pregnancy and the benefits of preventing seizures may outweigh any risks posed by using phenytoin.
Report any new or worsening symptoms to your doctor, such as: mood or behavior changes, depression, anxiety, or if you feel agitated, hostile, restless, hyperactive (mentally or physically), or have thoughts about suicide or hurting yourself.
You should not use phenytoin if you are allergic to it, or if you have ever had:
liver problems caused by phenytoin;
an allergy to similar medicines such as ethotoin, fosphenytoin, or mephenytoin; or
if you currently take delavirdine (Rescriptor).
To make sure phenytoin is safe for you, tell your doctor if you have ever had:
heart problems;
liver disease;
diabetes;
depression;
suicidal thoughts or actions;
a vitamin D deficiency or any other condition that causes thinning of the bones;
porphyria (a genetic enzyme disorder that causes symptoms affecting the skin or nervous system); or
if you are of Asian ancestry (you may need a special blood test to determine your risk for having a skin reaction to this medicine).
Some people have thoughts about suicide while taking this medicine. Your doctor will need to check your progress at regular visits. Your family or other caregivers should also be alert to changes in your mood or symptoms.
Seizure control is very important during pregnancy. Do not start or stop taking phenytoin without your doctor's advice if you are pregnant. Phenytoin may harm an unborn baby, but having a seizure during pregnancy could harm both mother and baby. Tell your doctor right away if you become pregnant while taking this medicine.
If you are pregnant, your name may be listed on a pregnancy registry to track the effects of phenytoin on the baby.
If you have taken this medicine during pregnancy, be sure to tell the doctor who delivers your baby about your phenytoin use. Both you and the baby may need to receive medications to prevent excessive bleeding during delivery and just after birth.
Phenytoin can make birth control pills less effective. Ask your doctor about using a non-hormonal birth control (condom, diaphragm with spermicide) to prevent pregnancy.
It may not be safe to breast-feed while using this medicine. Ask your doctor about any risk.
Take phenytoin exactly as prescribed by your doctor. Follow all directions on your prescription label and read all medication guides or instruction sheets. Your doctor may occasionally change your dose.
Swallow an extended-release capsule whole and do not crush, chew, break, or open it.
Phenytoin chewable tablets are not for once-per-day dosing. You must take them 2 or 3 times per day. Follow your doctor's dosing instructions very carefully.
Shake the oral suspension (liquid) before you measure a dose. Use the dosing syringe provided, or use a medicine dose-measuring device (not a kitchen spoon).
You may need frequent blood tests. You may also need a blood test when switching from one form to another. Visit your doctor regularly.
Tell your doctor if phenytoin does not seem to work as well in controlling your seizures. Do not stop using this medicine suddenly, even if you feel fine. Stopping suddenly may cause increased seizures. Follow your doctor's instructions about tapering your dose.
In case of emergency, wear or carry medical identification to let others know you have seizures.
Phenytoin can cause swelling in your gums. Brush and floss your teeth and visit your dentist regularly to help prevent this problem.
Store at room temperature away from moisture, light, and heat.
Usual Adult Dose for Seizures:
Oral (except suspension) Loading dose: Only when indicated for inpatients.
1 g orally divided in 3 doses (400 mg, 300 mg, 300 mg) given at 2 hour intervals. Then normal maintenance dosage started 24 hours after loading dose.
Initial dose: 100 mg extended release orally 3 times a day.
Maintenance dose: 100 mg orally 3 to 4 times a day. If seizure control is established with divided doses of three 100 mg capsules daily, once-a-day dosage with 300 mg of extended release phenytoin sodium may be considered. Alternatively, the dosage may need to be increased up to 200 mg orally 3 times a day, if necessary.
Suspension: Patients who have received no previous treatment may be started on 125 mg (one teaspoonful) of the suspension three times daily, and the dose is then adjusted to suit individual requirements. An increase to five teaspoonfuls daily may be made, if necessary.
IV: Do not exceed the infusion rate of 50 mg/min.
Loading dose: 10 to 15 mg/kg IV slowly.
Maintenance dose: 100 mg IV every 6 to 8 hours.
IM: Avoid the IM route due to erratic absorption.
Usual Adult Dose for Arrhythmias:
Loading Dose:
1.25 mg/kg IV every 5 minutes. May repeat up to a loading dose of 15 mg/kg, or
250 mg orally 4 times a day for 1 day, then 250 mg twice daily for 2 days
Maintenance Dose:
300 to 400 mg/day orally in divided doses 1 to 4 times a day
Usual Adult Dose for Status Epilepticus:
IV:
Loading dose: Manufacturer recommends 10 to 15 mg/kg by slow IV administration (at a rate not exceeding 50 mg/minute). Alternatively, generally accepted guidelines suggest 15 to 20 mg/kg by slow IV administration (at a rate not exceeding 50 mg/minute).
Maintenance rate: 100 mg orally or IV every 6 to 8 hours
Maximum rate: 50 mg/minute
Maintenance dose: IV or Oral: 100 mg every 6 to 8 hours
Usual Adult Dose for Neurosurgery:
Neurosurgery (prophylactic): 100 to 200 mg IM at about 4 hour intervals during surgery and the immediate postoperative period. (Note: While the manufacturer recommends IM administration, this route may cause severe local tissue destruction and necrosis. Some clinicians recommend the use of fosphenytoin if IM administration is necessary.) If IM administration is not necessary, accepted protocol has been 100 to 200 mg IV at about 4 hour intervals during surgery and the immediate postoperative period.
Usual Pediatric Dose for Seizures:
Status Epilepticus: Loading Dose:
Infants, Children: 15 to 20 mg/kg IV in a single or divided doses
Anticonvulsant: Loading Dose:
All ages: 15 to 20 mg/kg orally (based on phenytoin serum concentrations and recent dosing history). The oral loading dose should be given in 3 divided doses administered every 2 to 4 hours.
Anticonvulsant: Maintenance Dose:
(IV or oral) (Note: May initially divided daily dose into 3 doses/day, then adjust to suit individual requirements.)
Less than or equal to 4 weeks: Initial: 5 mg/kg/day in 2 divided doses
Usual: 5 to 8 mg/kg/day IV in 2 divided doses (may require dosing every 8 hours).
Greater than or equal to 4 weeks: Initial: 5 mg/kg/day in 2 to 3 divided doses
Usual: (may require up to every 8 hour dosing)
6 months to 3 years: 8 to 10 mg/kg/day
4 to 6 years: 7.5 to 9 mg/kg/day
7 to 9 years: 7 to 8 mg/kg/day
10 to 16 years: 6 to 7 mg/kg/day
Usual Pediatric Dose for Arrhythmias:
Greater than 1 year:
Loading Dose: 1.25 mg/kg IV every 5 minutes. May repeat up to a loading dose of 15 mg/kg.
Maintenance Dose: 5 to 10 mg/kg/day orally or IV in 2 to 3 divided doses
Take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.
Seek emergency medical attention or call the Poison Help line at 1-800-222-1222. An overdose of phenytoin can be fatal. Overdose symptoms may include twitching eye movements, slurred speech, loss of balance, tremor, muscle stiffness or weakness, nausea, vomiting, feeling light-headed, fainting, and slow or shallow breathing.
Avoid drinking alcohol while you are taking phenytoin. Alcohol use can increase your blood levels of phenytoin and may increase side effects. Daily alcohol use can decrease your blood levels of phenytoin, which can increase your risk of seizures.
Ask a doctor or pharmacist before using over-the-counter medicines such as cimetidine, omeprazole, St. John's wort, or vitamins and mineral supplements that contain folic acid.
Avoid driving or hazardous activity until you know how this medicine will affect you. Your reactions could be impaired.
Avoid taking antacids at the same time you take phenytoin. Antacids can make it harder for your body to absorb the medication.
Get emergency medical help if you have signs of an allergic reaction to phenytoin (hives, difficult breathing, swelling in your face or throat) or a severe skin reaction (fever, sore throat, burning in your eyes, skin pain, red or purple skin rash that spreads and causes blistering and peeling).
Seek medical treatment if you have a serious drug reaction that can affect many parts of your body. Symptoms may include: skin rash, fever, swollen glands, muscle aches, severe weakness, unusual bruising, or yellowing of your skin or eyes.
Report any new or worsening symptoms to your doctor, such as: mood or behavior changes, anxiety, panic attacks, trouble sleeping, or if you feel impulsive, irritable, agitated, hostile, aggressive, restless, hyperactive (mentally or physically), more depressed, or have thoughts about suicide or hurting yourself.
Call your doctor at once if you have:
slow or uneven heartbeats, chest pain, fluttering in your chest, and dizziness (like you might pass out);
any skin rash, no matter how mild;
fever, chills, sore throat, swollen glands;
red or swollen gums, mouth sores;
easy bruising, unusual bleeding, purple or red spots under your skin; or
liver problems - loss of appetite, upper stomach pain, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes).
Common phenytoin side effects may include:
drowsiness, confusion;
slurred speech;
abnormal eye movement; or
problems with balance or muscle movement.
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
Sometimes it is not safe to use certain medications at the same time. Some drugs can affect your blood levels of other drugs you take, which may increase side effects or make the medications less effective.
Many drugs can interact with phenytoin. Not all possible interactions are listed here. TELL YOUR DOCTOR ABOUT ALL OTHER MEDICINES YOU USE, and any you start or stop using during treatment. This includes prescription and over-the-counter medicines, vitamins, and herbal products.
Further informationRemember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use phenytoin only for the indication prescribed.
Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.
Medically reviewed by USARx EDITORIAL TEAM Last updated on 1/27/2021.
Source: Drugs.com Phenytoin (www.drugs.com/phenytoin.html).
Commonly reported side effects of phenytoin include: congenital anomalies. Other side effects include: hepatic necrosis, ataxia, confusion, constipation, depression, dizziness, drowsiness, fatigue, hypertrichosis, mental status changes, myasthenia, nervousness, numbness, tremor, tremor of hands, vertigo, excitement, irritability, mood changes, and restlessness. See below for a comprehensive list of adverse effects.
For the ConsumerApplies to phenytoin: oral capsule extended release, oral suspension, oral tablet chewable
Other dosage forms:
Along with its needed effects, phenytoin 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 while taking phenytoin:
More common
Rare
Incidence not known
Some side effects of phenytoin 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
Incidence not known
For Healthcare Professionals
Applies to phenytoin: compounding powder, injectable solution, oral capsule, oral capsule extended release, oral suspension, oral tablet chewable
CardiovascularCommon (1% to 10%): Hypotension, vasodilation, tachycardia
Uncommon (0.1% to 1%): Shock, cardiac arrest, syncope, cerebral hemorrhage, palpitation, sinus bradycardia, atrial flutter, bundle branch block, cardiomegaly, cerebral infarct, postural hypotension, pulmonary embolus, QT interval prolongation, thrombophlebitis, ventricular extrasystoles, congestive heart failure
Frequency not reported: Cardiovascular collapse, severe cardiotoxic reactions with atrial and ventricular conduction depression (including bradycardia and all degrees of heart block), asystole ventricular fibrillation, periarteritis nodosa
DermatologicVery common (10% or more): Rash (more serious and rare forms have included bullous, exfoliative or purpuric dermatitis, lupus erythematosus, Stevens-Johnson syndrome and toxic epidermal necrolysis), pruritus
Common (1% to 10%): Maculopapular rash, urticaria, sweating, skin discoloration, contact dermatitis, pustular rash, skin nodule, ecchymosis
Frequency not reported: Hirsutism, hypertrichosis, coarsening of the facial features, enlargement of the lips, Peyronie's disease. Dupuytren's contracture and drug rash with eosinophilia and systemic symptoms (DRESS), erythema multiforme, SJS/TEN risk in patients of Asian ancestry who have HLA-B 1502
EndocrineFrequency not reported: Decreased serum T4 and FT4, increased serum estradiol levels, gynecomastia, alterations in vitamin D metabolism
GastrointestinalVery common (10% or more): Nausea (13%)
Common (1% to 10%): Tongue disorder, dry mouth, vomiting, constipation
Uncommon (0.1% to 1%): Dyspepsia, diarrhea, anorexia, GI hemorrhage, increased salivation, tenesmus, tongue edema, dysphagia, flatulence, gastritis, ileus
Frequency not reported: Hypoesthesia of the tongue, gingival hyperplasia
GenitourinaryUncommon (0.1% to 1%): Urinary retention, oliguria, dysuria, vaginitis, albuminuria, genital edema, polyuria, urethral pain, urinary incontinence, vaginal moniliasis
Frequency not reported: Feeling of warmth or tingling in the groin, Peyronie's disease
HematologicCommon (1% to 10%): Ecchymosis
Uncommon (0.1% to 1%): Thrombocytopenia, anemia, leukocytosis, cyanosis, hypochromic anemia, leukopenia, lymphadenopathy, petechia
Frequency not reported: Granulocytopenia, agranulocytosis, pancytopenia (with or without bone marrow suppression), aplastic anemia
HepaticUncommon (0.1% to 1%): Liver function tests abnormal, kidney failure
Frequency not reported: Toxic hepatitis, hepatocellular damage
HypersensitivityFrequency not reported: Hypersensitivity syndrome, periarteritis nodosa
Postmarketing reports: Anaphylactoid reaction, anaphylaxis
ImmunologicUncommon (0.1% to 1%): Sepsis, flu syndrome, cryptococcosis
Frequency not reported: Immunoglobulin abnormalities
LocalCommon (1% to 10%): Injection site reaction, injection site pain
Uncommon (0.1% to 1%): Injection site inflammation, injection site edema, injection site hemorrhage
MetabolicUncommon (0.1% to 1%): Generalized edema, cachexia, diabetes insipidus
Frequency not reported: Hyperglycemia, appetite disorder, hypokalemia
MusculoskeletalCommon (1% to 10%): Back pain, chills, myasthenia
Uncommon (0.1% to 1%): Myopathy, leg cramps, arthralgia, myalgia, muscular weakness, muscle twitching, muscle spasms
Frequency not reported: Systemic lupus erythematosus, polyarthritis, Purple Glove Syndrome
Nervous systemVery common (10% or more): Nystagmus (59%), dizziness (31%), somnolence (27%), ataxia (18%)
Common (1% to 10%): Headache, stupor, incoordination, paresthesia, extrapyramidal syndrome, tremor, vertigo, brain edema, tinnitus, taste perversion (including metallic taste), taste loss, reflexes decreased, reflexes increased, migraine, slurred speech, dysarthria, intracranial hypertension, hyperesthesia, hyporeflexia
Uncommon (0.1% to 1%): Twitching, Babinski sign positive, circumoral paresthesia, hemiplegia, hypotonia, convulsion, meningitis, CNS depression, hypokinesia, hyperkinesia, brain edema, paralysis, aphasia, coma, myoclonus, acute brain syndrome, encephalitis, subdural hematoma, encephalopathy, akathisia
Frequency not reported: CNS depression, dyskinesia (including chorea), dystonia and asterixis similar to those induced by phenothiazines or other neuroleptic drugs, drowsiness, motor twitching, tonic seizures, sensory peripheral polyneuropathy (in patients receiving long-term therapy)
OcularCommon (1% to 10%): Diplopia, amblyopia, blurred vision, visual impairment
Uncommon (0.1% to 1%): Photosensitivity reaction, photophobia, eye pain, mydriasis, visual field defect
OtherCommon (1% to 10%): Asthenia, deafness, accidental injury, fever, face edema, hyperacusis, parosmia, ear pain
Uncommon (0.1% to 1%): Malaise
RenalCommon (1% to 10%): Pelvic pain
Uncommon (0.1% to 1%): Kidney failure
RespiratoryCommon (1% to 10%): Pneumonia
Uncommon (0.1% to 1%): Pharyngitis, sinusitis, hyperventilation, rhinitis, apnea, aspiration pneumonia, asthma, dyspnea, atelectasis, cough increased, sputum increased, epistaxis, hypoxia, pneumothorax, hemoptysis, bronchitis
Postmarketing reports: Respiratory arrest (sometimes fatal)
PsychiatricCommon (1% to 10%): Agitation, thinking abnormal, nervousness, depression
Uncommon (0.1% to 1%): Confusion, insomnia, depersonalization, psychosis, emotional lability, personality disorder, hostility, amnesia, neurosis, euphoric mood
Medically reviewed by USARx EDITORIAL TEAM Last updated on 1/27/2021.
Source: Drugs.com Phenytoin (www.drugs.com/phenytoin.html).
March 23, 2021
March 19, 2021
February 15, 2021
February 15, 2021
September 25, 2020
September 2, 2020
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