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Fosphenytoin (Injection)

Generic name: fosphenytoin [ fos-FEN-i-toin ]
Brand name: Cerebyx
Drug class: Hydantoin anticonvulsants

Medically reviewed by Drugs.com. Last updated on Nov 25, 2023.

Injection route(Solution)

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 .

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. This medicine is an anticonvulsant that works in the brain tissue to stop seizures.

Fosphenytoin injection also used for short-term substitution for oral phenytoin. This medicine should only be used when taking phenytoin by mouth is not possible.

This medicine 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 this medicine, the following should be considered:

Allergies

Tell your doctor if you have ever had any unusual or allergic reaction to this medicine 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.

Pediatric

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 performed to date have not demonstrated pediatric-specific problems that would limit the usefulness of Sesquient™ injection for short-term substitution for oral phenytoin in children 2 years of age and older. Safety and efficacy have been established.

Geriatric

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.

Breast Feeding

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 this medicine, 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 this medicine 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.

Using this medicine 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.

Using this medicine 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.

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 this medicine 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 this medicine, 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 this medicine. Make sure you tell your doctor if you have any other medical problems, especially:

Proper use of fosphenytoin

A nurse or other trained health professional will give you this medicine in a hospital. This medicine 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 this medicine 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 this medicine. 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 this medicine 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 this medicine while you are also taking delavirdine (Rescriptor®). Using these medicines together may cause delavirdine to not work as well for you.

This medicine may increase your risk for heart or blood vessel problems. Check with your doctor right away if you have blurred vision, chest pain, confusion, lightheadedness, dizziness, or fainting, fast or irregular heartbeat, trouble breathing, or unusual tiredness or weakness.

This medicine may cause some people to become dizzy, lightheaded, faint, or less alert than they are normally. Make sure you know how you react to this medicine 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 this medicine without first checking with your doctor. Stopping the medicine suddenly may cause your seizures to return or to occur more often.

Serious skin reactions (eg, toxic epidermal necrolysis, Stevens-Johnson syndrome, acute-generalized exanthematous pustulosis) can occur with this medicine. Check with your doctor right away if you or your child have blistering, peeling, or loose skin, chills, cough, diarrhea, itching, joint or muscle pain, red irritated eyes, red skin lesions, often with a purple center, sore throat, sores, ulcers, or white spots in the mouth or on the lips, or unusual tiredness or weakness while you are using this medicine.

Tell your doctor right away if you or your child develop a black, tarry stools, chest pain, chills, cough, fever, rash, swollen, painful, or tender lymph glands in the neck, armpit, or groin, painful or difficult urination, sore throat, sores, ulcers, or white spots on the lips or in the mouth, unusual bleeding or bruising, or yellow eyes or skin after using this medicine. These may be symptoms of a serious and life-threatening condition called drug reaction with eosinophilia and systemic symptoms (DRESS).

This medicine 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 this medicine.

This medicine may cause liver problems. Check with your doctor right away if you or your child have a dark-colored urine, general feeling of tiredness or weakness, headache, light-colored stools, stomach pain continuing, vomiting, or yellow eyes or skin.

Fosphenytoin can temporarily lower the number of white blood cells in your blood, increasing the chance of getting an infection. It can also lower the number of platelets, which are necessary for proper blood clotting. If this occurs, there are certain precautions you can take, especially when your blood count is low, to reduce the risk of infection or bleeding:

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.

This medicine may cause purple glove syndrome. Tell your doctor right away if you have skin discoloration, pain, or swelling at the injection site after receiving this medicine.

This medicine 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 this medicine. 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 this medicine.

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.

Side Effects of fosphenytoin

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:

More common

Less common

Rare

Incidence not known

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:

More common

Less common

Rare

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.

Commonly used brand name(s)

In the U.S.

Available Dosage Forms:

Therapeutic Class: Anticonvulsant

Chemical Class: Hydantoin (class)

Further information

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