Phenytoin

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.

Applies to phenytoin: oral capsule extended release, oral suspension, oral tablet chewable

Other dosage forms:

• injection solution

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

• Decreased coordination
• mental confusion
• nervousness
• slurred speech
• trouble with breathing, speaking, or swallowing
• unsteadiness, trembling, or other problems with muscle control or coordination

Rare

• Inability to move the eyes
• increased blinking or spasms of the eyelid
• shakiness and unsteady walk shakiness in the legs, arms, hands, or feet
• sticking out of the tongue
• trembling or shaking of the hands or feet
• twitching, twisting, or uncontrolled repetitive movements of the tongue, lips, face, arms, or legs
• uncontrolled twisting movements of the neck, trunk, arms, or legs
• unusual facial expressions

Incidence not known

• Abdominal or stomach pain
• bleeding gums
• blistering, peeling, or loosening of the skin
• blisters, hives, or itching
• bloating of the abdomen or stomach
• blood in the urine or stools
• bloody, black, or tarry stools
• chest pain
• chills
• cough or hoarseness
• dark urine
• diarrhea
• difficulty with moving
• fainting spells
• fever with or without chills
• general feeling of discomfort or illness
• general feeling of tiredness or weakness
• hair loss
• headache
• high fever
• irregular heartbeat
• irritation in the mouth
• joint or muscle pain
• light-colored stools
• lower back or side pain
• muscle stiffness
• nausea or vomiting
• numbness, tingling, or pain in the hands or feet
• painful or difficult urination
• pale skin
• pinpoint red spots on the skin
• red skin lesions, often with a purple center
• red, irritated eyes
• redness and swelling of the gums
• skin blisters
• skin rash
• sore throat
• sores, ulcers, or white spots on the lips or in the mouth
• swollen, painful, or tender lymph glands in the neck, armpit, or groin
• unusual bleeding or bruising
• unusual tiredness
• upper right abdominal or stomach pain
• weakness
• weight loss
• yellow eyes or skin

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

• Trouble sleeping
• uncontrolled eye movements

Incidence not known

• Difficulty having a bowel movement (stool)
• enlarged lips
• feeling of constant movement of self or surroundings
• increased hair growth on the forehead, back, arms, or legs
• pain of the penis on erection
• sensation of spinning

Applies to phenytoin: compounding powder, injectable solution, oral capsule, oral capsule extended release, oral suspension, oral tablet chewable

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

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

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

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

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

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

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

Frequency not reported: Toxic hepatitis, hepatocellular damage

Frequency not reported: Hypersensitivity syndrome, periarteritis nodosa

Postmarketing reports: Anaphylactoid reaction, anaphylaxis

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

Frequency not reported: Immunoglobulin abnormalities

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

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

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

Frequency not reported: Hyperglycemia, appetite disorder, hypokalemia

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

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)

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

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

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

Uncommon (0.1% to 1%): Malaise

Common (1% to 10%): Pelvic pain

Uncommon (0.1% to 1%): Kidney failure

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)

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