What are the side effects of fosphenytoin (Cerebyx)?

The most common side effects in adults are itching, uncontrolled eye movements, dizziness, drowsiness, and problems controlling your muscles. In children, the most common side effects are vomiting, uncontrolled eye movements, and problems controlling their muscles. Some people have reported severe burning and/or a "pins and needles" feeling after getting fosphenytoin (Cerebyx). In most cases, this went away within a day. Your provider might be able to slow down or stop your infusion to help improve these symptoms. In rare cases, some people have experienced swelling, discoloration (color changes), and pain at the injection site ("[purple glove syndrome](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3139342/)"). Sometimes, these symptoms appear several days after the injection.

fosphenytoin

Q: What is fosphenytoin (Cerebyx)?

Fosphenytoin (Cerebyx) is an injectable [antiseizure medication](https://www.goodrx.com/conditions/epilepsy/epilepsy-treatment-options) that's used to prevent and treat seizures during neurosurgery (brain surgery) in children and adults. It's also used to treat [tonic-clonic status epilepticus](https://www.epilepsy.com/complications-risks/emergencies/status-epilepticus), which is a type of seizure that's repeated or lasts 5 minutes or longer. Additionally, fosphenytoin (Cerebyx) can be temporarily used in place of oral [phenytoin (Dilantin)](https://www.goodrx.com/phenytoin/what-is), when you can't take anything by mouth.

Q: How does fosphenytoin (Cerebyx) work to treat seizures?

After fosphenytoin (Cerebyx) is injected, your body changes it into the active medication phenytoin. It's not fully known how phenytoin works for seizures, but researchers think it lowers abnormal signals between nerve cells in the brain.

Q: How is fosphenytoin (Cerebyx) given?

Fosphenytoin (Cerebyx) is typically infused into the veins (intravenous or IV) by a healthcare provider. In some cases, your provider might give it as an injection into the muscles. Your dose depends on things like your body weight and your response to the medication. Your provider will make sure you get the right fosphenytoin (Cerebyx) dose at the right time.

Q: Does fosphenytoin (Cerebyx) have any serious risks?

Yes. Fosphenytoin (Cerebyx) can cause serious heart problems, like low blood pressure and abnormal heart rhythm. The risk is higher when it's given too quickly. For your safety, your provider will monitor your heart and breathing while you're getting this medication. In addition, fosphenytoin (Cerebyx) can cause serious allergic reactions. These can include life-threatening skin reactions, swelling, and [anaphylaxis](https://www.goodrx.com/conditions/anaphylaxis) (closing of the throat). Get medical help right away if you notice fever, rash, swelling in your face, or trouble breathing. Fosphenytoin (Cerebyx) can also raise your blood sugar levels, cause liver damage, and affect your blood cell counts.

Generic Cerebyx

Used for Epilepsy

Fosphenytoin (Cerebyx) is an injectable medication used to treat and prevent seizures in both children and adults. This medication has many risks and possible side effects, including uncontrolled eye movements, dizziness, and trouble moving your muscles. Fosphenytoin (Cerebyx) is typically given by a healthcare provider.

Reviewed by:

Kristianne Hannemann, PharmD

Allison Gourley, PharmD

Last reviewed on September 18, 2022

What is Fosphenytoin (Cerebyx)?

What is Fosphenytoin (Cerebyx) used for?

To treat or prevent seizures

Are you looking for information on celecoxib (Celebrex) instead?

Drug facts

Common Brands	Cerebyx
Drug Class	Antiepileptic
Controlled Substance Classification	Not a controlled medication
Generic Status	No lower-cost generic available
Availability	Prescription only

Common Brands

Cerebyx

Drug Class

Antiepileptic

Controlled Substance Classification

Not a controlled medication

Generic Status

No lower-cost generic available

Availability

Prescription only

Common questions about Fosphenytoin

Fosphenytoin is an injectable antiseizure medication that's used to prevent and treat seizures during neurosurgery (brain surgery) in children and adults. It's also used to treat tonic-clonic status epilepticus, which is a type of seizure that's repeated or lasts 5 minutes or longer. Additionally, Fosphenytoin can be temporarily used in place of oral phenytoin (Dilantin), when you can't take anything by mouth.

After Fosphenytoin is injected, your body changes it into the active medication phenytoin. It's not fully known how phenytoin works for seizures, but researchers think it lowers abnormal signals between nerve cells in the brain.

Fosphenytoin is typically infused into the veins (intravenous or IV) by a healthcare provider. In some cases, your provider might give it as an injection into the muscles. Your dose depends on things like your body weight and your response to the medication. Your provider will make sure you get the right Fosphenytoin dose at the right time.

The most common side effects in adults are itching, uncontrolled eye movements, dizziness, drowsiness, and problems controlling your muscles. In children, the most common side effects are vomiting, uncontrolled eye movements, and problems controlling their muscles. Some people have reported severe burning and/or a "pins and needles" feeling after getting Fosphenytoin. In most cases, this went away within a day. Your provider might be able to slow down or stop your infusion to help improve these symptoms. In rare cases, some people have experienced swelling, discoloration (color changes), and pain at the injection site ("purple glove syndrome"). Sometimes, these symptoms appear several days after the injection.

Yes. Fosphenytoin can cause serious heart problems, like low blood pressure and abnormal heart rhythm. The risk is higher when it's given too quickly. For your safety, your provider will monitor your heart and breathing while you're getting this medication. In addition, Fosphenytoin can cause serious allergic reactions. These can include life-threatening skin reactions, swelling, and anaphylaxis (closing of the throat). Get medical help right away if you notice fever, rash, swelling in your face, or trouble breathing. Fosphenytoin can also raise your blood sugar levels, cause liver damage, and affect your blood cell counts.

Fosphenytoin (Cerebyx) dosage

Typical dosage for Fosphenytoin (Cerebyx)

Interactions between Fosphenytoin (Cerebyx) and other drugs

Fosphenytoin (Cerebyx) may interact with certain medications or supplements. Always let your doctor and pharmacist know about any other medications or supplements (including prescribed and over-the-counter medications, vitamins, and dietary or herbal supplements) that you are currently taking. The list below does not include all possible drug interactions with Fosphenytoin (Cerebyx). Please note that only the generic name of each medication is listed below.

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.

Artemether
Atazanavir
Bepridil
Boceprevir
Cisapride
Cobicistat
Daclatasvir
Dasabuvir
Delamanid
Delavirdine
Doravirine
Dronedarone
Elbasvir
Elvitegravir
Fostemsavir
Grazoprevir
Isavuconazonium
Lorlatinib
Lurasidone
Maraviroc
Mesoridazine
Ombitasvir
Paritaprevir
Pimozide
Piperaquine
Praziquantel
Ranolazine
Rilpivirine
Ritonavir
Sparfloxacin
Telaprevir
Tenofovir Alafenamide
Terfenadine
Thioridazine
Ziprasidone

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.

Abemaciclib
Abiraterone Acetate
Acalabrutinib
Afatinib
Alfentanil
Alpelisib
Amiodarone
Amisulpride
Anagrelide
Apazone
Apixaban
Apomorphine
Apremilast
Aprepitant
Aripiprazole
Arsenic Trioxide
Avapritinib
Axitinib
Beclamide
Bedaquiline
Bendamustine
Benzhydrocodone
Berotralstat
Betrixaban
Bictegravir
Bosutinib
Brexpiprazole
Brigatinib
Buprenorphine
Bupropion
Buserelin
Cabozantinib
Calcifediol
Cannabidiol
Capmatinib
Carbamazepine
Cariprazine
Cenobamate
Ceritinib
Chloroquine
Chlorpheniramine
Cisatracurium
Clarithromycin
Clofazimine
Clozapine
Cobimetinib
Codeine
Copanlisib
Crizotinib
Cyclophosphamide
Dabigatran Etexilate
Dabrafenib
Darolutamide
Dasatinib
Deferasirox
Deflazacort
Degarelix
Deslorelin
Desogestrel
Deutetrabenazine
Dexamethasone
Diazepam
Diazoxide
Dienogest
Dihydrocodeine
Dolutegravir
Domperidone
Donepezil
Dopamine
Doxorubicin
Doxorubicin Hydrochloride Liposome
Drospirenone
Duvelisib
Efavirenz
Elexacaftor
Eliglustat
Encorafenib
Entrectinib
Enzalutamide
Eravacycline
Erdafitinib
Erlotinib
Escitalopram
Eslicarbazepine Acetate
Estradiol
Ethinyl Estradiol
Ethosuximide
Ethynodiol
Etonogestrel
Etravirine
Everolimus
Exemestane
Ezogabine
Fedratinib
Fentanyl
Fingolimod
Fluoxetine
Fluvastatin
Formoterol
Fosaprepitant
Foscarnet
Fosnetupitant
Fostamatinib
Gefitinib
Gestodene
Gilteritinib
Glasdegib
Glecaprevir
Gonadorelin
Goserelin
Halothane
Hemin
Histrelin
Hydrocodone
Hydroxychloroquine
Hydroxyzine
Ibrutinib
Idelalisib
Ifosfamide
Imatinib
Infliximab
Inotuzumab Ozogamicin
Irinotecan
Irinotecan Liposome
Istradefylline
Itraconazole
Ivabradine
Ivacaftor
Ivosidenib
Ixabepilone
Ixazomib
Ketoconazole
Lamotrigine
Lapatinib
Larotrectinib
Ledipasvir
Lefamulin
Lemborexant
Lenvatinib
Letermovir
Levofloxacin
Levoleucovorin
Levonorgestrel
Lidocaine
Linagliptin
Lofexidine
Lopinavir
Lumateperone
Lurbinectedin
Macimorelin
Macitentan
Manidipine
Medroxyprogesterone
Meperidine
Mestranol
Methadone
Methotrexate
Metronidazole
Miconazole
Midostaurin
Mifepristone
Mirtazapine
Moxifloxacin
Nafarelin
Naloxegol
Neratinib
Netupitant
Nifedipine
Nilotinib
Nimodipine
Nintedanib
Nitisinone
Nomegestrol
Norelgestromin
Norethindrone
Norgestimate
Norgestrel
Olaparib
Ondansetron
Orlistat
Osilodrostat
Osimertinib
Oxaliplatin
Oxcarbazepine
Oxycodone
Ozanimod
Paclitaxel
Palbociclib
Paliperidone
Panobinostat
Pasireotide
Pazopanib
Pemigatinib
Pentazocine
Perampanel
Pexidartinib
Pibrentasvir
Pimavanserin
Pitolisant
Ponatinib
Ponesimod
Posaconazole
Pralsetinib
Pretomanid
Quetiapine
Regorafenib
Relugolix
Reserpine
Ribociclib
Rifampin
Rimegepant
Ripretinib
Rocuronium
Roflumilast
Rolapitant
Romidepsin
Saquinavir
Segesterone
Selpercatinib
Selumetinib
Sertraline
Sevoflurane
Simeprevir
Siponimod
Sofosbuvir
Solifenacin
Sonidegib
Sorafenib
Sotalol
Stiripentol
St John's Wort
Sufentanil
Sulpiride
Sunitinib
Tacrolimus
Tamoxifen
Tasimelteon
Tazemetostat
Temsirolimus
Tezacaftor
Theophylline
Thiotepa
Ticagrelor
Tivozanib
Tofacitinib
Tolvaptan
Trabectedin
Tramadol
Trazodone
Triclabendazole
Triptorelin
Tucatinib
Ubrogepant
Ulipristal
Upadacitinib
Valbenazine
Vandetanib
Velpatasvir
Vemurafenib
Venetoclax
Vilazodone
Vincristine
Vincristine Sulfate Liposome
Vinflunine
Voclosporin
Vorapaxar
Voriconazole
Vortioxetine
Voxelotor
Voxilaprevir
Zanubrutinib
Zuclopenthixol

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.