Cerebyx Side Effects

Generic name: fosphenytoin

Medically reviewed by Drugs.com. Last updated on Apr 30, 2023.

Note: This document contains side effect information about fosphenytoin. Some dosage forms listed on this page may not apply to the brand name Cerebyx.

Applies to fosphenytoin: injection solution.

Serious side effects of Cerebyx

Along with its needed effects, fosphenytoin (the active ingredient contained in Cerebyx) 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 or nurse immediately if any of the following side effects occur while taking fosphenytoin:

More common

• Blurred vision
• confusion
• dizziness, faintness, or lightheadedness when getting up suddenly from a lying or sitting position
• feeling of warmth or heat
• flushing or redness of the skin, especially on the face and neck
• headache
• sweating
• unusual tiredness or weakness

Less common

• Anxiety
• bruising
• burning, crawling, itching, numbness, prickling, "pins and needles", or tingling feelings
• changes in patterns and rhythms of speech
• dark-colored urine
• difficulty with speaking
• drooling
• dry mouth
• fast, pounding, or irregular heartbeat or pulse
• hyperventilation
• irritability
• itching skin
• lack of coordination
• large, flat, blue, or purplish patches in the skin
• light-colored stools
• loss of balance control
• muscle trembling, jerking, or stiffness
• nervousness
• problems with movement, walking, or speech
• restlessness
• seizures
• shakiness in the legs, arms, hands, or feet
• shuffling walk
• slurred speech
• stiffness of the limbs
• trouble breathing
• trouble with sleeping
• twisting movements of the body
• uncontrolled movements, especially of the face, neck, and back
• unsteadiness, trembling, or other problems with muscle control or coordination
• vomiting
• yellow eyes or skin

Rare

• Absence of or decrease in body movement
• aggressive or angry
• agitation
• black, tarry stools
• bleeding gums
• bleeding, blistering, burning, coldness, discoloration of the skin, feeling of pressure, hives, infection, inflammation, itching, lumps, numbness, pain, rash, redness, scarring, soreness, stinging, swelling, tenderness, tingling, ulceration, or warmth at the injection site
• blistering, burning, crusting, dryness, or flaking of the skin
• blood in the urine or stools
• bloody nose
• bluish color of the fingernails, lips, skin, palms, or nail beds
• body aches or pain
• bone pain
• burning while urinating
• change in consciousness
• change in personality
• change in the ability to see colors, especially blue or yellow
• change in the color of the treated skin
• chest pain, discomfort, or tightness
• cloudy urine
• cold, clammy skin
• congestion
• cough or hoarseness
• cough producing mucus
• coughing or spitting up blood
• crying
• decrease in frequency of urination
• decrease in the amount of urine
• deep or fast breathing with dizziness
• delusions
• dementia
• depression
• diarrhea
• difficulty in passing urine (dribbling)
• difficulty with breathing
• difficulty with moving
• difficulty with swallowing
• dilated neck veins
• dizziness, fainting, or lightheadedness
• drowsiness
• dryness or soreness of the throat
• dysphoria
• euphoria
• eye pain
• feeling of unreality
• feeling that others are watching you or controlling your behavior
• feeling that others can hear your thoughts
• feeling, seeing, or hearing things that are not there
• fever or chills
• flushed, dry skin
• frequent urination
• fruit-like breath odor
• general feeling of discomfort or illness
• general physical wasting or malnutrition associated with severe illness
• greatly increased frequency of urination or amount of urine
• headache, severe and throbbing
• hives or welts
• inability to move the legs or arms
• inability to sit still
• increase in body movements
• increase in heart rate
• increased hunger
• increased sensitivity of the skin to sunlight
• increased thirst
• increased urination
• increased volume of pale, dilute urine
• increased watering of the mouth
• irregular breathing
• itching, scaling, severe redness, soreness, or swelling of the skin
• joint pain
• leg cramps
• loss of appetite
• loss of bladder control
• loss of consciousness
• loss of memory
• loss of strength or energy
• lower back or side pain
• muscle aches, pains, or stiffness
• muscle twitching or jerking
• muscular tenderness, wasting, or weakness
• nausea or vomiting
• need to keep moving
• no blood pressure or pulse
• not breathing
• numbness of the feet, hands, and around the mouth
• numbness or tingling in the face, arms, hands, feet, or lips
• pain or tenderness around the eyes and cheekbones
• pale skin
• paralysis of one side of the body
• paranoia
• pinpoint red spots on the skin
• pounding in the ears
• problems with memory
• quick to react or overreact emotionally
• rapid breathing
• rapid heartbeat
• rapid weight gain
• rapidly changing moods
• rash with flat lesions or small raised lesions on the skin
• redness or other discoloration of the skin
• rhythmic movement of the muscles
• seizures
• sense of detachment from self or body
• severe constipation
• severe headache
• severe mood or mental changes
• severe pain in the chest
• severe sunburn
• severe vomiting
• shivering
• sleeplessness
• small lumps under the skin
• small red or purple spots on the skin
• sneezing
• sores, ulcers, or white spots on the lips or in the mouth
• spots on your skin resembling a blister or pimple
• stiff neck
• stomach pain
• stopping of heart
• stuffy or runny nose
• sudden onset of severe breathing difficulty
• sunken eyes
• swelling of the face, fingers, feet, ankles, or lower legs
• swelling of the tongue
• swollen joints
• swollen, painful, or tender lymph glands in the neck, armpit, or groin
• twisting movements of body
• unable to sleep
• unconsciousness
• uncontrolled movements, especially of the face, neck, and back
• unexplained weight loss
• unusual behavior
• unusual bleeding or bruising
• unusual weak feeling
• voice changes
• vomiting of blood or material that looks like coffee grounds
• weakness or heaviness of the legs
• weight gain
• wrinkled skin

Incidence not known

• Puffiness or swelling of the eyelids or around the eyes, face, lips or tongue
• twitching, twisting, uncontrolled repetitive movements of the tongue, lips, face, arms, or legs

Other side effects of Cerebyx

Some side effects of fosphenytoin 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

• Continuing ringing or buzzing or other unexplained noise in the ears
• decreased awareness or responsiveness
• hearing loss
• severe sleepiness
• sleepiness or unusual drowsiness
• uncontrolled eye movements

Less common

• Back pain
• change in taste or bad, unusual, or unpleasant (after) taste
• change in vision
• double vision
• feeling of constant movement of self or surroundings
• impaired vision
• lack or loss of strength
• pelvic pain
• seeing double
• sensation of spinning

Rare

• Acid or sour stomach
• belching
• bigger, dilated, or enlarged pupils (black part of eye)
• bloated
• burning feeling in the chest or stomach
• burning, dry, or itching eyes
• change in color vision
• difficulty having a bowel movement (stool)
• difficulty seeing at night
• discharge, excessive tearing
• ear pain
• excess air or gas in the stomach or bowels
• frequent urge to defecate
• full feeling
• heartburn
• increased sense of hearing
• increased sensitivity of the eyes to light
• indigestion
• itching of the vagina or genital area
• loss of taste
• pain during sexual intercourse
• passing gas
• redness, pain, swelling of the eye, eyelid, or inner lining of the eyelid
• stomach discomfort, upset, or pain
• straining while passing stool
• tenderness in the stomach area
• thick, white vaginal discharge with no odor or with a mild odor
• transient, mild, or pleasant aromatic odor
• vaginal yeast infection
• weight loss

For Healthcare Professionals

Applies to fosphenytoin: injectable solution, intravenous solution.

General

The more commonly reported adverse reactions have included pruritus, nystagmus, dizziness, somnolence, vomiting, and ataxia.

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^[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]

Hypersensitivity

Frequency not reported: Hypersensitivity syndrome, periarteritis nodosa, SJS/TEN risk in patients of Asian ancestry who have HLA-B 1502

Postmarketing reports: Anaphylactoid reaction, anaphylaxis, angioedema^[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]

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

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

Metabolic

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

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

Immunologic

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

Frequency not reported: Immunoglobulin abnormalities^[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^[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, taste loss,reflexes decreased, reflexes increased, migraine, speech disorder, 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)

Postmarketing reports: Dyskinesia^[Ref]

Other

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

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

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]

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]

Endocrine

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

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.

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