The rate of IV fosphenytoin sodium administration should not exceed 150 mg phenytoin sodium equivalents (PE) per minute in adults and 2 mg PE/kg/min (or 150 mg PE/min, whichever is slower) in pediatric patients because of the risk of severe hypotension and cardiac arrhythmias. Careful cardiac monitoring is needed during and after administering IV fosphenytoin sodium. Although the risk of cardiovascular toxicity increases with infusion rates above the recommended infusion rate, these events have also been reported at or below the recommended infusion rate. Reduction in rate of administration or discontinuation of dosing may be needed .
Medically reviewed by Drugs.com. Last updated on Apr 29, 2019.
Commonly used brand name(s)
In the U.S.
Available Dosage Forms:
Therapeutic Class: Anticonvulsant
Chemical Class: Hydantoin (class)
Uses for fosphenytoin
Fosphenytoin injection is used to control certain types of seizures (convulsions) in the treatment of epilepsy. It is also used to prevent and treat seizures that occur during brain surgery. Fosphenytoin is an anticonvulsant that works in the brain tissue to stop seizures.
Fosphenytoin is to be given only by or under the direct supervision of a doctor.
Before using fosphenytoin
In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For fosphenytoin, the following should be considered:
Tell your doctor if you have ever had any unusual or allergic reaction to fosphenytoin or any other medicines. Also tell your health care professional if you have any other types of allergies, such as to foods, dyes, preservatives, or animals. For non-prescription products, read the label or package ingredients carefully.
Appropriate studies performed to date have not demonstrated pediatric-specific problems that would limit the usefulness of Cerebyx® injection in children.
Appropriate studies have not been performed on the relationship of age to the effects of fosphenytoin injection in the pediatric population. Safety and efficacy have not been established.
Appropriate studies on the relationship of age to the effects of fosphenytoin injection have not been performed in the geriatric population. However, elderly patients are more likely to have age-related liver, kidney, or heart problems, which may require caution and an adjustment in the dose for patients receiving fosphenytoin injection.
There are no adequate studies in women for determining infant risk when using this medication during breastfeeding. Weigh the potential benefits against the potential risks before taking this medication while breastfeeding.
Interactions with medicines
Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are receiving fosphenytoin, it is especially important that your healthcare professional know if you are taking any of the medicines listed below. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.
Using fosphenytoin with any of the following medicines is not recommended. Your doctor may decide not to treat you with this medication or change some of the other medicines you take.
- Tenofovir Alafenamide
Using fosphenytoin with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.
- Abiraterone Acetate
- Arsenic Trioxide
- Dabigatran Etexilate
- Doxorubicin Hydrochloride Liposome
- Eslicarbazepine Acetate
- Ethinyl Estradiol
- Inotuzumab Ozogamicin
- Irinotecan Liposome
- St John's Wort
- Vincristine Sulfate Liposome
Using fosphenytoin with any of the following medicines may cause an increased risk of certain side effects, but using both drugs may be the best treatment for you. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.
- Folic Acid
- Valproic Acid
Interactions with food/tobacco/alcohol
Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.
Using fosphenytoin with any of the following may cause an increased risk of certain side effects but may be unavoidable in some cases. If used together, your doctor may change the dose or how often you use fosphenytoin, or give you special instructions about the use of food, alcohol, or tobacco.
Other medical problems
The presence of other medical problems may affect the use of fosphenytoin. Make sure you tell your doctor if you have any other medical problems, especially:
- Blood or bone marrow problems (eg, agranulocytosis, leukopenia, or thrombocytopenia) or
- Diabetes or
- Heart failure or
- Hypotension (low blood pressure) or
- Lymphadenopathy (lymph node problems) or
- Porphyria (an enzyme problem)—Use with caution. May make these conditions worse.
- Heart block (eg, Adams-Stokes syndrome, AV block, or sinoatrial block) or
- Sinus bradycardia (slow heartbeat)—Should not be used in patients with these conditions.
- Hypoalbuminemia (low albumin in the blood) or
- Kidney disease or
- Liver disease—Use with caution. The effects may be increased because of slower removal from the body.
Proper use of fosphenytoin
A nurse or other trained health professional will give you fosphenytoin in a hospital. Fosphenytoin is given as a shot into one of your muscles or through a needle placed in one of your veins.
Your doctor will only give you a few doses of fosphenytoin until your condition improves. You will be switched to an oral medicine that works the same way. If you have any concerns about this, talk to your doctor.
Precautions while using fosphenytoin
It is very important that your doctor check your progress closely while you are receiving fosphenytoin. This is to see if the medicine is working properly and to allow for a change in the dose. Blood tests may be needed to check for any unwanted effects.
Using fosphenytoin while you are pregnant can harm your unborn baby. Use an effective form of birth control to keep from getting pregnant. If you think you have become pregnant while using the medicine, tell your doctor right away. Your doctor may want you to join a pregnancy registry for patients taking a seizure medicine.
Do not receive fosphenytoin while you are also taking delavirdine (Rescriptor®). Using these medicines together may cause delavirdine to not work as well for you.
Fosphenytoin may cause some people to become dizzy, lightheaded, faint, or less alert than they are normally. Make sure you know how you react to fosphenytoin before you drive, use machines, or do anything else that could be dangerous if you are dizzy or are not alert and able to see well.
Do not stop using fosphenytoin without first checking with your doctor. Stopping the medicine suddenly may cause your seizures to return or to occur more often.
Serious skin reactions can occur with fosphenytoin. Check with your doctor right away if you or your child have blistering, peeling, or loose skin, red skin lesions, severe acne or skin rash, sores or ulcers on the skin, a fever, or chills while you are using fosphenytoin.
Tell your doctor right away if you or your child develop a fever, rash, swollen, painful, or tender lymph glands in the neck, armpit, or groin, unusual bleeding or bruising, or yellow eyes or skin after using fosphenytoin. These may be symptoms of a serious and life-threatening condition called drug reaction with eosinophilia and systemic symptoms (DRESS).
Fosphenytoin may cause serious allergic reactions, including angioedema. These can be life-threatening and require immediate medical attention. Tell your doctor right away if you or your child have a rash, itching, hoarseness, trouble breathing, trouble swallowing, or any swelling of your hands, face, or mouth after using fosphenytoin.
Tell your doctor right away if your skin feels like it is burning, crawling, or itching, or if you have numbness, prickling, "pins and needles", or tingling feelings after receiving fosphenytoin injection.
Fosphenytoin may cause purple glove syndrome. Tell your doctor right away if you have skin discoloration, pain, or swelling at the injection site after receiving fosphenytoin.
Fosphenytoin may affect blood sugar levels. If you notice a change in the results of your blood or urine sugar tests or if you have any questions, check with your doctor.
Birth control pills may not work while you are using fosphenytoin. To keep from getting pregnant, use another form of birth control along with your birth control pills. Other forms include a condom, a diaphragm, or a contraceptive foam or jelly.
Avoid drinking alcohol while you are receiving fosphenytoin.
Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.
Fosphenytoin side effects
Along with its needed effects, a medicine 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:
- Blurred vision
- 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
- unusual tiredness or weakness
- burning, crawling, itching, numbness, prickling, "pins and needles", or tingling feelings
- changes in patterns and rhythms of speech
- difficulty with speaking
- dry mouth
- fast, pounding, or irregular heartbeat or pulse
- itching skin
- lack of coordination
- large, flat, blue, or purplish patches in the skin
- loss of balance control
- muscle trembling, jerking, or stiffness
- problems with movement, walking, or speech
- shakiness in the legs, arms, hands, or feet
- shortness of breath
- shuffling walk
- slurred speech
- stiffness of the limbs
- 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
- Abdominal or stomach pain
- absence of or decrease in body movement
- aggressive or angry
- 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 or discomfort
- cloudy urine
- cold, clammy skin
- cough or hoarseness
- cough producing mucus
- coughing or spitting up blood
- decrease in frequency of urination
- decrease in the amount of urine
- deep or fast breathing with dizziness
- difficulty in passing urine (dribbling)
- difficulty with breathing
- difficulty with moving
- difficulty with swallowing
- dilated neck veins
- dizziness, fainting, or lightheadedness
- dryness or soreness of the throat
- 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
- 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 of the skin
- redness or other discoloration of the skin
- rhythmic movement of the muscles
- 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
- small lumps under the skin
- small red or purple spots on the skin
- sores, ulcers, or white spots on the lips or in the mouth
- spots on your skin resembling a blister or pimple
- stiff neck
- stopping of heart
- stuffy or runny nose
- sudden onset of severe breathing difficulty
- sudden shortness of breath or troubled breathing
- 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
- tightness of the chest
- troubled breathing with exertion
- twisting movements of body
- unable to sleep
- 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
Some side effects 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:
- 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
- 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
- Acid or sour stomach
- bigger, dilated, or enlarged pupils (black part of eye)
- 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 intestines
- frequent urge to defecate
- full feeling
- increased sense of hearing
- increased sensitivity of the eyes to light
- 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
Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.
Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.
Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.
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More about fosphenytoin
- Side Effects
- During Pregnancy
- Dosage Information
- Drug Interactions
- Pricing & Coupons
- En Español
- Drug class: hydantoin anticonvulsants
- FDA Alerts (1)
Other brands: Cerebyx