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Phenytoin Side Effects

Medically reviewed by Drugs.com. Last updated on Feb 26, 2024.

Applies to phenytoin: oral capsule extended release, oral suspension, oral tablet chewable. Other dosage forms:

Serious side effects of Phenytoin

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

Other side effects of Phenytoin

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.

Cardiovascular

Common (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[Ref]

Dermatologic

Very 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[Ref]

Endocrine

Frequency not reported: Decreased serum T4 and FT4, increased serum estradiol levels, gynecomastia, alterations in vitamin D metabolism[Ref]

Gastrointestinal

Very 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[Ref]

Genitourinary

Uncommon (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[Ref]

Hematologic

Common (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[Ref]

Hepatic

Uncommon (0.1% to 1%): Liver function tests abnormal, kidney failure

Frequency not reported: Toxic hepatitis, hepatocellular damage[Ref]

Hypersensitivity

Frequency not reported: Hypersensitivity syndrome, periarteritis nodosa

Postmarketing reports: Anaphylactoid reaction, anaphylaxis[Ref]

Immunologic

Uncommon (0.1% to 1%): Sepsis, flu syndrome, cryptococcosis

Frequency not reported: Immunoglobulin abnormalities[Ref]

Local

Common (1% to 10%): Injection site reaction, injection site pain

Uncommon (0.1% to 1%): Injection site inflammation, injection site edema, injection site hemorrhage[Ref]

Metabolic

Uncommon (0.1% to 1%): Generalized edema, cachexia, diabetes insipidus

Frequency not reported: Hyperglycemia, appetite disorder, hypokalemia[Ref]

Musculoskeletal

Common (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[Ref]

Nervous system

Very 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)[Ref]

Ocular

Common (1% to 10%): Diplopia, amblyopia, blurred vision, visual impairment

Uncommon (0.1% to 1%): Photosensitivity reaction, photophobia, eye pain, mydriasis, visual field defect[Ref]

Other

Common (1% to 10%): Asthenia, deafness, accidental injury, fever, face edema, hyperacusis, parosmia, ear pain

Uncommon (0.1% to 1%): Malaise[Ref]

Renal

Common (1% to 10%): Pelvic pain

Uncommon (0.1% to 1%): Kidney failure[Ref]

Respiratory

Common (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)[Ref]

Psychiatric

Common (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[Ref]

References

1. (2001) "Product Information. Dilantin (phenytoin)." Parke-Davis

2. Cerner Multum, Inc. "UK Summary of Product Characteristics."

3. Pharmaceutical Society of Australia (2006) APPGuide online. Australian prescription products guide online. http://www.appco.com.au/appguide/default.asp

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.