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Cerebyx: Full Drug Profile

Medically reviewed by Min Clinic Staff | Updated: January 2026

Cerebyx - General Information

Cerebyx is a water-soluble phenytoin prodrug used only in hospitals for the treatment of epileptic seizures. It works by slowing down impulses in the brain that cause seizures. Its main mechanism is to block frequency-dependent, use-dependent and voltage-dependent neuronal sodium channels, and therefore limit repetitive firing of action potentials.

 

Pharmacology of Cerebyx

Cerebyx is a water-soluble phenytoin prodrug used only in hospitals for the treatment of epileptic seizures. Following parenteral administration of fosphenytoin, fosphenytoin is converted to the anticonvulsant phenytoin. For every mmol of fosphenytoin administered, one mmol of phenytoin is produced. The pharmacological and toxicological effects of fosphenytoin include those of phenytoin.

 

Cerebyx for patients

 

Cerebyx Interactions

No drugs are known to interfere with the conversion of fosphenytoin to phenytoin. Conversion could be affected by alterations in the level of phosphatase activity, but given the abundance and wide distribution of phosphatases in the body it is unlikely that drugs would affect this activity enough to affect conversion of fosphenytoin to phenytoin. Drugs highly bound to albumin could increase the unbound fraction of fosphenytoin. Although, it is unknown whether this could result in clinically significant effects, caution is advised when administering Cerebyx with other drugs that significantly bind to serum albumin.

The pharmacokinetics and protein binding of fosphenytoin, phenytoin, and diazepam were not altered when diazepam and Cerebyx were concurrently administered in single submaximal doses.

The most significant drug interactions following administration of Cerebyx are expected to occur with drugs that interact with phenytoin. Phenytoin is extensively bound to serum plasma proteins and is prone to competitive displacement. Phenytoin is metabolized by hepatic cytochrome P450 enzymes and is particularly susceptible to inhibitory drug interactions because it is subject to saturable metabolism. Inhibition of metabolism may produce significant increases in circulating phenytoin concentrations and enhance the risk of drug toxicity. Phenytoin is a potent inducer of hepatic drug-metabolizing enzymes.

The most commonly occurring drug interactions are listed below:

  • Drugs that may increase plasma phenytoin concentrations include: acute alcohol intake, amiodarone, chboramphenicol, chlordiazepoxide, cimetidine, diazepam, dicumarol, disulfiram, estrogens, ethosuximide, fluoxetine, H2-antagonists, halothane, isoniazid, methylphenidate, phenothiazines, phenylbutazone, salicylates, succinimides, sulfonamides, tolbutamide, trazodone.
  • Drugs that may decrease plasma phenytoin concentrations include: carbamazepine, chronic alcohol abuse, reserpine.
  • Drugs that may either increase or decrease plasma phenytoin concentrations include: phenobarbital, vaiproic acid, and sodium valproate. Similarly, the effects of phenytoin on phenobarbital, valproic acid and sodium plasma valproate concentrations are unpredictable.
  • Although not a true drug interaction, tricyclic antidepressants may precipitate seizures in susceptible patients and Cerebyx dosage may need to be adjusted.
  • Drugs whose efficacy is impaired by phenytoin include: anticoagulants, corticosteroids, coumarin, digitoxin, doxycycline, estrogens, furosemide, oral contraceptives, rifampin, quinidine, theophylline, vitamin D.

Monitoring of plasma phenytoin concentrations may be helpful when possible drug interactions are suspected.

Drug/Laboratory Test Interactions

Phenytoin may decrease serum concentrations of 14. It may also produce artifactually low results in dexamethasone or metyrapone tests. Phenytoin may also cause increased serum concentrations of glucose, alkaline phosphatase, and gamma glutamyl transpeptidase (GGT).

Care should be taken when using immunoanalytical methods to measure plasma phenytoin concentrations following Cerebyx administration.

 

Cerebyx Contraindications

Cerebyx is contraindicated in patients who have demonstrated hypersensitivity to Cerebyx or its ingredients, or to phenytoin or other hydantoins.

Because of the effect of parenteral phenytoin on ventricular automaticity, Cerebyx is contraindicated in patients with sinus bradycardia, sino-atrial block, second and third degree A-V block, and Adams-Stokes syndrome.

 

Additional information about Cerebyx

Cerebyx Indication: For the control of generalized convulsive status epilepticus and prevention and treatment of seizures occurring during neurosurgery. It can also be substituted, short-term, for oral phenytoin. Mechanism Of Action: Cerebyx is a prodrug of phenytoin and accordingly, its anticonvulsant effects are attributable to phenytoin. Phenytoin acts on sodium channels on the neuronal cell membrane, limiting the spread of seizure activity and reducing seizure propagation. By promoting sodium efflux from neurons, phenytoin tends to stabilize the threshold against hyperexcitability caused by excessive stimulation or environmental changes capable of reducing membrane sodium gradient. This includes the reduction of post-tetanic potentiation at synapses. Loss of post-tetanic potentiation prevents cortical seizure foci from detonating adjacent cortical areas. Drug Interactions: Alprazolam Possible increased levels of the hydantoin, decrease of benzodiazepine Chlordiazepoxide Possible increased levels of the hydantoin, decrease of benzodiazepine Clorazepate Possible increased levels of the hydantoin, decrease of benzodiazepine Diazepam Possible increased levels of the hydantoin, decrease of benzodiazepine Estazolam Possible increased levels of the hydantoin, decrease of benzodiazepine Flurazepam Possible increased levels of the hydantoin, decrease of benzodiazepine Lorazepam Possible increased levels of the hydantoin, decrease of benzodiazepine Midazolam Possible increased levels of the hydantoin, decrease of benzodiazepine Oxazepam Possible increased levels of the hydantoin, decrease of benzodiazepine Quazepam Possible increased levels of the hydantoin, decrease of benzodiazepine Temazepam Possible increased levels of the hydantoin, decrease of benzodiazepine Triazolam Possible increased levels of the hydantoin, decrease of benzodiazepine Cisplatin The antineoplasic agent decreases the effect of hydantoin Methotrexate The antineoplasic agent decreases the effect of hydantoin Bleomycin The antineoplasic agent decreases the effect of hydantoin Carboplatin The antineoplasic agent decreases the effect of hydantoin Carmustine The antineoplasic agent decreases the effect of hydantoin Vinblastine The antineoplasic agent decreases the effect of hydantoin Aminophylline Decreased effect of both products Dyphylline Decreased effect of both products Theophylline Decreased effect of both products Oxtriphylline Decreased effect of both products Warfarin Increased hydantoin levels and risk of bleeding Acenocoumarol Increased hydantoin levels and risk of bleeding Dicumarol Increased hydantoin levels and risk of bleeding Anisindione Increased hydantoin levels and risk of bleeding Voriconazole The hydantoin decreases the effect of voriconazole Vigabatrin Vigabatrin decreases the effect of hydantoin Vecuronium Phenytoin decreases the effect of muscle relaxant Tubocurarine Phenytoin decreases the effect of muscle relaxant Tacrolimus The hydantoin decreases the effect of tacrolimus Telithromycin Telithromycin may possibly increase this agent's effect/toxicity Pancuronium Phenytoin decreases the effect of muscle relaxant Atracurium Phenytoin decreases the effect of muscle relaxant Doxacurium Phenytoin decreases the effect of muscle relaxant Gallamine Triethiodide Phenytoin decreases the effect of muscle relaxant Metocurine Phenytoin decreases the effect of muscle relaxant Mivacurium Phenytoin decreases the effect of muscle relaxant Amiodarone Amiodarone increases the effect of hydantoin Aprepitant This CYP3A4 inducer decreases the effect of aprepitant Betamethasone The enzyme inducer decreases the effect of the corticosteroid Capecitabine Capecitabine increases the effect of hydantoin Chloramphenicol Increases phenytoin, modifies chloramphenicol Cimetidine Cimetidine increases the effect of hydantoin Ciprofloxacin Ciprofloxacin decreases the hydantoin effect Clarithromycin Clarithromycin increases the effect and toxicity of phenytoin Cortisone acetate The enzyme inducer decreases the effect of the corticosteroid Dexamethasone The enzyme inducer decreases the effect of the corticosteroid Fludrocortisone The enzyme inducer decreases the effect of the corticosteroid Hydrocortisone The enzyme inducer decreases the effect of the corticosteroid Methylprednisolone The enzyme inducer decreases the effect of the corticosteroid Paramethasone The enzyme inducer decreases the effect of the corticosteroid Prednisolone The enzyme inducer decreases the effect of the corticosteroid Prednisone The enzyme inducer decreases the effect of the corticosteroid Triamcinolone The enzyme inducer decreases the effect of the corticosteroid Trimethoprim Trimethoprim increases the effect of hydantoin Trioxsalen The hydantoin decreases the effect of psoralene Thiotepa Possible increase in thiotepa levels Ticlopidine Ticlopidine increases the effect of hydantoin Topiramate Increased phenytoin/decreased topiramate Chlorotrianisene The enzyme inducer decreases the effect of hormones Diethylstilbestrol The enzyme inducer decreases the effect of hormones Clomifene The enzyme inducer decreases the effect of hormones Estradiol The enzyme inducer decreases the effect of hormones Conjugated Estrogens The enzyme inducer decreases the effect of hormones Estriol The enzyme inducer decreases the effect of hormones Estrone The enzyme inducer decreases the effect of hormones Estropipate The enzyme inducer decreases the effect of hormones Medroxyprogesterone The enzyme inducer decreases the effect of hormones Megestrol The enzyme inducer decreases the effect of hormones Sertraline Sertraline increases the effect of hydantoin Quinestrol The enzyme inducer decreases the effect of hormones Chlorpheniramine The antihistamine increases the effect of hydantoin Chlorpheniramine The antihistamine increases the effect of hydantoin Clozapine Hydantoin decreases the effect of clozapine Cyclosporine The hydantoin decreases the effect of cyclosporine Delavirdine The anticonvulsant decreases the effect of delavirdine Diazoxide Diazoxide decreases the hydantoin effect Disopyramide The hydantoin decreases the effect of disopyramide Disulfiram Disulfiram increases the effect of phenytoin Divalproex sodium Valproate increases the effect of hydantoin Dopamine Risk of severe hypotension Doxycycline The anticonvulsant decreases the effect of doxycycline Irinotecan The hydantoin decreases the effect of irinotecan Imatinib The hydantoin decreases the levels of imatinib Gefitinib This CYP3A4 inducer may reduce gefitinib plasma concentrations and pharmacological effects Fluvoxamine Fluvoxamine increases the effect of hydantoin Folic Acid Folic acid decreases the levels of hydantoin Furosemide The hydantoin decreases the effect of furosemide Gabapentin Gabapentin increases the effect of hydantoin Fluorouracil Fluorouracil increases the effect of hydantoin Fluoxetine Fluoxetine increases the effect of phenytoin Fluconazole Fluconazole increases the effect of hydantoin Felodipine The hydantoin decreases the effect of felodipine Felbamate Increased phenytoin levels and decreased felbamate levels Ethinyl Estradiol This product may cause a slight decrease of contraceptive effect Nisoldipine Phenytoin decreases the efficiency of nisoldipine Metyrapone The combination renders the test invalid Mexiletine The hydantoin decreases the effect of mexiletine Isoniazid Isoniazid increases the effect of phenytoin Itraconazole Phenytoin decreases the effect of itraconazole Lamotrigine Phenytoin may reduce levels of lamotrigine Levodopa The hydantoin decreases the effect of levodopa Levonorgestrel Phenytoin decreases the contraceptive effect Lopinavir Levels of both drugs are affected Mebendazole The hydantoin decreases the efficiency of mebendazole Mestranol This product may cause a slight decrease of contraceptive effect Methadone The hydantoin decreases the effect of methadone Methoxsalen The hydantoin decreases the effect of psoralene Mirtazapine The hydantoins may reduce mirtazapine plasma concentrations and pharmacological effects Norethindrone This product may cause a slight decrease of contraceptive effect Sulfamethizole The sulfonamide increases the effect of hydantoin Sulfadiazine The sulfonamide increases the effect of hydantoin Sucralfate Sucralfate decreases the effect of hydantoin Sirolimus The hydantoin decreases sirolimus levels Quinidine The anticonvulsant decreases the effect of quinidine Quinupristin This combination presents an increased risk of toxicity Rifampin Rifampin decreases the effect of hydantoin Omeprazole Omeprazole increases the effect of hydantoin Oxcarbazepine Oxcarbazepine increases the effect of hydantoin Oxyphenbutazone The NSAID increases the hydantoin effect Phenylbutazone The NSAID increases the hydantoin effect Posaconazole Modifications of drug levels for both agents Quetiapine Phenytoin decreases the effect of quetiapine Food Interactions: Avoid alcohol. Take with food. Do not take calcium, aluminum, magnesium or Iron supplements within 2 hours of taking this medication. Generic Name: Fosphenytoin Synonyms: Fosphenytoin sodium; (3-Phosphoryloxymethyl)phenytoin; Fosfenitoina [inn-spanish]; Fosphenytoine [inn-french]; Fosphenytoinum [inn-latin] Drug Category: Anticonvulsants Drug Type: Small Molecule; Approved Other Brand Names containing Fosphenytoin: Prodilantin; Cerebyx; Absorption: Fosphenytoin is completely bioavailable following lM administration. Toxicity (Overdose): Nausea, vomiting, lethargy, tachycardia, bradycardia, asystole, cardiac arrest, hypotension, syncope, hypocalcemia, metabolic acidosis, and death have been reported in cases of overdosage with fosphenytoin. The median lethal dose of fosphenytoin given intravenously in mice and rats was 156 mg PE/kg and approximately 250 mg PE/kg, or about 0.6 and 2 times, respectively, the maximum human loading dose on a mg/m2 basis. Signs of acute toxicity in animals included ataxia, labored breathing, ptosis, and hypoactivity. Protein Binding: Extensively bound (95% to 99%) to human plasma proteins, primarily albumin. Biotransformation: Hepatic. Half Life: Fosphenytoin has a half-life of approximately 15 minutes. Dosage Forms of Cerebyx: Liquid Intravenous Liquid Intravenous Chemical IUPAC Name: [2,5-dioxo-4,4-di(phenyl)imidazolidin-1-yl]methyl dihydrogen phosphate Chemical Formula: C16H15N2O6P Fosphenytoin on Wikipedia: https://en.wikipedia.org/wiki/Fosphenytoin Organisms Affected: Humans and other mammals