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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 1/3/2022.
Source: Drugs.com Phenytoin (www.drugs.com/phenytoin.html).
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